I was sorely tempted to headline this post “Alien megastructures discovered in Ballard,” but that would have meant sinking low into the sort of clickbait science that concerns Dr. James Davenport. Davenport, a research scientist at the University of Washington, gave a talk about the topic at the most recent gathering of Astronomy on Tap Seattle.
Dr. James Davenport. UW photo.
Davenport described himself as a big fan of science, and noted that to be such one needs to be OK with failure.
“Being wrong is just nature telling you, no, try again. Come up with a better idea, a better explanation for how the universe is working,” Davenport said. “If you love science, you have to love the struggle and you have to love truth.”
Davenport believes that it’s important to communicate about science, but often that leads to misconceptions or outright lies. Sometimes the misinformation is silly stuff, like trying to pump up the hype about a lunar eclipse by calling it the super blood wolf coyote Moon. Sometimes it’s just wrong. An example is what now seems like the annual return of social media posts announcing that Mars is going to appear as large as a full Moon in the night sky. This particular hoax may date back to 2003, when Mars actually was closer to Earth than it had been in some 60 thousand years. The falsehood was based on a nugget of truth, and Mars was an especially good target for astronomers that summer, but if you looked up it was still just a bright red dot in the sky. When someone doesn’t see that giant Mars they might conclude that science is stupid.
“Little by little we chip away at your interest, your excitement, your enthusiasm, your belief, and your trust in science as an institution,” Davenport lamented.
Outrageous headlines
You’ve probably read many stories for which you found that the headline had little to do with the actual content. The purpose of the headline is to make you look. Davenport noted this phenomenon related to media coverage of Boyajian’s star, which brightens and dims in odd and unexpected ways. Scientists kicked around a lot of possible explanations for this observation. Maybe it’s a weird dust cloud or passing comets or debris from an asteroid collision. Someone even suggested a Dyson sphere or some other sort of “alien megastructure.” This grabbed the attention of the headline writers, and articles in Scientific American, the Washington Post, The Atlantic, Discover magazine, and others featured headlines about the possible discovery of alien megastructures, though the articles essentially said, “probably not.”
“There’s real science here but oh, golly, we need to be careful about reporting it,” Davenport said. “We have an obligation as scientists to be really careful and I worry that we’re not.” The truth about Boyajian’s star has yet to be figured out.
Where’s the rigor?
Another challenge for science communication is that there are some sites out there that are not exactly rigorous. For example, Davenport shared the following tweet from a site called Physics and Astronomy Zone.
You probably know that Pluto has not been reinstated. The tweet links to an old article—from April Fool’s Day. Also attached to that article are a slew of links to “stories” about the gifts men really want, amazing rebates for seniors, alien DNA in marijuana, and lots of other nonsense. It’s pure clickbait.
“This is a machine to get you to click on things, to get your eyeballs on things, to get you to engage with things so they make a few pennies,” Davenport said. “They do that a million times a day.”
There’s a lot of churn there. @zonephysics has more than 900 thousand Twitter followers.
“This is a huge impact for nonsense,” Davenport said. “Where is the celebration of truth?”
Few legitimate scientists have nearly so many Twitter followers. Neil deGrasse Tyson has more than 13 million, and Bad Astronomer Phil Plait has more than 615 thousand. As of this writing Davenport has 2,917. Seattle Astronomy has 2,135.
What to do
Davenport figures there are three things we can do to battle against the spread of pseudo-science and downright rubbish:
Communicate about science; don’t leave it to pseudoscientists spread misinformation
Share and intervene. Point out bunk when you see it.
Get the help of technology and tech companies to figure out how to weed out bad sources and find a way to remove the incentive for clickbait.
“We need other solutions besides just eyeball time equals dollars equals the only thing that matters on the Internet,” Davenport said. “We need tools that help us optimize for things beside just eyeball time. We need tools that help us figure out what’s the most efficient way to get knowledge across. What’s the most efficient way to help us identify bad actors who are spreading misinformation and intervening when people are trying to share that content.”
There’s some heavy lifting ahead.
“We need to do science outreach. We need help from everyone to spread truth and identify falsehoods. And we need the help of technology,” Davenport concluded. See below to watch his entire talk!
Astronomy on Tap Seattle is organized by graduate students in astronomy at the University of Washington. They’re taking a break in December and their next event will be held January 22, 2020.
The most recent gathering of Astronomy on Tap Seattle promised to take us inside the way science is really done, and delivered with tales of unexpected successes and a colossal fail that left a team of cosmologists with cosmic egg on their faces.
Leah Fulmer
Leah Fulmer, a second year graduate student in astronomy at the University of Washington, gave a talk titled “Falling with Style: How Astronomy’s Most Intriguing Discoveries Happen by Accident.” Fulmer noted that astronomers have lots of choices when it comes to their research. They can select which part of the sky to examine, what to look at, how long to look, how often to look, and in which wavelengths of light to look, just to name a few. There’s lots of potential there.
“Every time we look at the universe in a new way we discover new phenomena that we never even expected to see,” she said. Fulmer shared three historical examples of such scientific serendipity.
The first was the detection of the cosmic microwave background (CMB) back in the 1960s. At the time it was theorized that 400,000 years after the Big Bang the CMB would have left its energy throughout the universe as a result of the event. Arno Penzias and Robert Wilson had access to a big radio telescope and were working on doing some radio astronomy. The problem was that they couldn’t tweak out some pervasive and persistent noise from their observations. Meanwhile down the road some theorists at Princeton were trying to figure out how to detect evidence of the CMB. Penzias and Wilson had already done it!
“By accident they took this telescope that NASA had built for satellite communication, they stuck it out there, and they found literally the origins of the universe,” Fulmer said. “This changed our understanding of astronomy and physics as we know it and it was a really, really big deal, just by looking at something in a new wavelength.”
More recently the operators of the Hubble Space Telescope decided to pick out an empty, black part of the sky and have the scope stare at it for 100 hours. Many scientists thought this was a bit daft.
The Hubble Deep Field. Image credit: Robert Williams and the Hubble Deep Field Team (STScI) and NASA/ESA.
“They found what’s now known as the Hubble Deep Field,” Fulmer said. “They found an incredible plethora of galaxies that they never expected to see.” It revolutionized our understanding of the number of galaxies in the universe and added greatly to the types, shapes, and sizes of galaxies that we know about.
The Kepler Space Telescope found thousands of exoplanets and collected data on so many things that scientists couldn’t possibly look at all of them. They enlisted citizen scientists through Zooniverse to help examine objects.
Participants looked at the data and among their findings is an oddly behaving star for which its light curves defy explanation. We now know of it as “Tabby’s Star,” after astronomer Tabetha Boyajian, who wrote the paper about the discovery.
“To this day we don’t actually know what this star is,” Fulmer said. There have been lots of ideas about the odd light curves, from a random pack of asteroids that might be irregularly blocking light, some sort of cosmic catastrophe that kicked up debris, and even giant space structures built by an unknown civilization.
“It’s very precarious for an astronomer to suggest that this might be aliens,” Fulmer laughed, noting that the media would have a field day with that sort of thing.
The potential for discovering strange new things in the universe is about to increase. The Large Synoptic Survey Telescope is scheduled to go online in a few years, and when it does it will collect petabytes of data, doing a complete sweep of the sky every few nights for a decade.
Fulmer said a big part of her job in the project will be to help “develop an algorithm that is going to be able to systematically identify the things that we’ve never seen before.” That’s a tall order, combing all of that data for things we know about, things that have been theorized, and those that come out of the blue.
“We don’t what surprises we might find,” Fulmer said, “but that’s what makes it so exciting.”
Oops
Samantha Gilbert, a first-year graduate student in astronomy at the UW, told a story about a colossal and embarrassing failure. Her talk was titled, “Leaving the Competition in the Dust: A CMB Case Study.”
“The story I want to tell you tonight has everything: It has science. It has drama. It has egos. It has really esoteric vector math,” Gilbert said to laughter. “It encapsulates some of the things that are really wrong with how some people do science today.”
The story also involves the cosmic microwave background. Cosmologists are trying to figure out what happened between the Big Bang and the formation of the CMB 400,000 years later. A leading theory is that there was a period of inflation in the moments after the Big Bang during which the universe expanded rapidly. If that happened, it would have created gravitational waves, and those waves would have left behind a pattern in the CMB that we could recognize, called “B-mode polarization.”
A map of the cosmic microwave background. Image credit: NASA/WMAP Science Team
“B-mode polarization is an extraordinarily difficult thing to detect,” Gilbert said, “but proving it exists, proving that inflation really happened by detecting the traces of inflationary gravitational waves” would be Nobel Prize-worthy.
That’s where the intrigue starts. One group striving for this discovery had an experiment called BICEP (Background Imaging of Cosmic Extragalactic Polarization), which was followed by BICEP2, which had more sensitive detectors than the first version and more of them. They found what they were looking for. In fact, the signal of B-mode polarization was even stronger than anticipated. The team declared the discovery during a 2014 news conference at Harvard, issued a video, broke out the bubbly, and in general whipped up lots of hoopla about the discovery.
In the following months some 250 papers were published in response to BICEP2. One of them was from BICEP’s main competitor, the Planck Experiment, and their point was that BICEP’s discovery was bunk and that what they detected was not B-mode polarization, but cosmic dust.
“The fact that BICEP2 had so confidently announced a result that was so quickly disproven had a rippling effect throughout the community,” Gilbert said. “Scientists were horrified because they thought, ‘now the public is going to discredit us, they’re not going to trust us.’ Journalists were also horrified because they felt they had a role in spreading disinformation.”
They were also seeing an ugly side of the scientific community.
The need for speed
How did this happen? BICEP principal investigator Brian Keating wrote a book about their process, titled Losing the Nobel Prize (W.W. Norton & Company, 2018). Gilbert summarized their decision-making.
She said BICEP2 only looked at one wavelength of light so they could get the results as quickly as possible. They knew about the possibility of cosmic dust, but didn’t have the tools to distinguish between dust and B-mode polarization. The Planck folks were thought to have the data, and BICEP asked them to share. They declined.
This led BICEP to jump to the conclusion that Planck also had evidence of B-mode polarization and were aiming to scoop them on the discovery and dash their dreams of a Nobel Prize. So they hurried to make the announcement. This might have worked out OK, if they’d been right, but the BICEP group made one other glaring error.
“They actually hadn’t put their paper through peer review,” Gilbert noted, generating groans among the science-savvy audience at Astronomy on Tap.
“That is a no-no,” she understated. “That is a bad thing to do because peer review is what makes science credible in the first place. It’s a really important check against the dissemination of junk science. You really need other scientists to independently assess your results.”
Gilbert said the bad decisions were all motivated by fear.
“Overly competitive environments are part and parcel of an individualistic conception of science and an individualistic conception of science says that the most important thing is to get a result before your competition,” she said. “When that’s the environment that you’re working in you tend to make decisions based on fear.”
“I would argue that the reason that BICEP2 made these decisions based on fear is that they were operating in such a toxically competitive environment that it became dysfunctional,” Gilbert said. “Whether you think competition is really good for science, really bad, or somewhere in between, I think that this case study shows us that it’s really worth thinking about the ways that we systemically and interpersonally encourage competition, and how that might jeopardize our ways of knowing.”
Gilbert said there’s hope for the future. The hunt for B-mode polarization continues, and BICEP and Planck are teaming up going forward, combining their resources and know-how in the work.
“Competition might be the most efficient way to A result, but collaboration is probably the most efficient way to a RELIABLE result,” she said.
Astronomy on Tap Seattle is organized by graduate students in astronomy at the University of Washington. More info:
It takes a lot of detective work to figure out the nature of a type Ia supernova. Celestial Pig Pens and new tricks from old telescopes are contributing to the effort. That’s what we learned at the most recent meeting of Astronomy on Tap Seattle.
Messy Siblings: Supernovae in Binary Systems
Dr. Melissa Graham is a project science analyst for the Large Synoptic Survey Telescope, working out of the Astronomy Department at the University of Washington. Her main research focus is supernovae. In particular, she’s doing a lot of work on type Ia supernovae, which occur in binary star systems. One of the stars involved will be a carbon-oxygen white dwarf star.
“It’s a star that wasn’t massive enough to fuse anything else inside the carbon layers,” Graham explained. Outer layers of hydrogen and helium are thrown off in a planetary nebula phase, so the carbon and oxygen are what’s left.
Melissa Graham. UW photo.
“Carbon-oxygen white dwarf stars are very compact, very dense, about the size of the Earth but they can be up to about 1.4 times the mass of the Sun,” Graham said. These stars are pretty stable as stars go, so they don’t blow up under normal circumstances.
“When we do see these kind of supernovae that are clearly the explosion of carbon-oxygen white dwarf stars we have to wonder why,” she said. It turns out there are two possible scenarios. The binary can be a pair of carbon-oxygen white dwarf stars that spiral in on each other, merge, and then explode. Or the binary can include one white dwarf and a more typical hydrogen-rich companion star.
“In this case the companion star can feed material onto this carbon-oxygen white dwarf star, might make it go over 1.4 solar masses, become unstable, and then explode,” Graham said.
Which is which?
The key to figuring out which of these scenarios actually occurred is to take a look at the area around the supernova. If the companion is a more hydrogen-rich companion star, the neighborhood can get a little messy.
“It’s sort of like a celestial Pig Pen star that leaves a lot of material lying around,” Graham said. A blast from a supernova can interact with this material and cause it to brighten. The trouble is that astronomers typically only observe type Ia supernovae for a couple of months; they fade quickly. So if this extra material is far away from the event, they might not see the interaction. The answer is patience, to look at the supernova sites for up to 2-3 years after.
Graham did exactly that, using the Hubble Space Telescope to keep an eye on the locations of 65 type Ia supernovae.
“Out of these 65, I very luckily found one” in which there was brightening much later. They checked the spectrum of the light and found hydrogen, a sure sign that the companion in this particular type Ia supernova was a Pig Pen. Graham suspects that up to five percent of such explosions involve messy sibling stars.
Graham looks forward to having the Large Synoptic Survey Telescope (LSST) come on line. She expects it will find some 10 million supernovae in a decade.
“This marks a massive increase in our ability to both find and characterize supernovae,” she said.
Old scope, new tricks
While we wait for LSST an old workhorse telescope is doing interesting work in a similar vein. Professor Eric Bellm of the UW works with the Zwicky Transient Facility (ZTF), which uses the 48-inch telescope at Palomar observatory in California. The scope is a Schmidt, completed in 1948, and for years it was the largest Schmidt telescope in the world. It’s main function at first was to use its wide-field view of the sky to create maps that helped astronomers point Palomar Mountain’s 200-inch Hale Telescope.
Eric Bellm. UW photo.
The 48-inch was used to do numerous sky surveys over the years. It discovered many asteroids, and Mike Brown used it to find the dwarf planets he used to kill Pluto. The old photographic plates gave way to modern CCDs, and Bellm became the project scientist for the Zwicky Transient Facility—named for astronomer Fritz Zwicky, a prolific discoverer of supernovae—in 2011.
They outfitted the scope with a new camera with 16 CCDs that are four inches per side. They got some big filters for it and put in a robotic arm that could change the filters without getting in the way of the camera. They started surveying in March of last year and can photograph much of the sky on any given night.
“That’s letting us look for things that are rare, things that are changing quickly, things that are unusual,” Bellm said.
Examples of what the ZTF has found include a pair of white dwarfs that are spinning rapidly around each other, with a period of just seven minutes. They can see the orbits decay because of gravitational wave radiation. It has discovered more than 100 young type 1a supernovae. And it found an asteroid with the shortest “year” of any yet discovered; its orbit is entirely within that of Venus.
It’s doing the same sort of work that the LSST will do when it comes online.
“It’s super cool that we’ve got this more than 70 year old telescope that we’re doing cutting-edge science with thanks to the advances of technology,” Bellm said.
Astronomy on Tap Seattle is organized by graduate students in astronomy at the University of Washington, and typically meets on the fourth Wednesday of each month at Peddler Brewing Company in Ballard. The next event is set for September 25.
As we look back at the 50th anniversary of the Apollo 11 Moon landing, Toby Smith notes that the most interesting science that came out of the mission was a bit of a surprise. Smith, a senior lecturer in astronomy at the University of Washington, gave a talk at the most recent meeting of Astronomy on Tap Seattle.
“There’s only one reason Apollo existed—to beat the Soviet Union to the surface of the Moon,” Smith noted. Few considered the mission to be scientific. “It wasn’t fully embraced by the scientific community even in its day, even among planetary scientists.”
But they figured as long as they were there, they should do some sort of science.
“This little bit of science they did fundamentally changed how we view not only the Moon, but the Earth-Moon system and our solar system,” Smith said.
The Apollo 11 landing site, the Sea of Tranquility on the Moon, is essentially an ancient lava flow, a featureless plain of cooled volcanic rock, Smith said. Think of it like Big Island of Hawaii, except you don’t really see the solidified lava on the Moon. The surface is soft, ground down and rounded off into a soft powder by billions of years of impacts. As Neil Armstrong observed just after his first step, it has the consistency of flour. That consistency almost accidentally led to the mission’s best science.
An Apollo Lunar Sample Return container on display
at the Destination: Moon exhibit at the St. Louis Science
Center in 2018. (Photo: Greg Scheiderer)
Armstrong spent about 15 minutes of the two-and-a-half hour Moon walk picking up rocks and putting them into a box. At the end he collected nine scoops of lunar regolith and dumped it into the Apollo Lunar Sample Return Container (a fancy NASA term for the case for rocks) as sort of a packing material so the larger rocks wouldn’t clatter around. If they’d taken any styrofoam peanuts he might have used those instead.
Naturally, when this material was brought back to Earth, the scientists looked at it, and Smith said it just might be the most studied geological sample ever.
Smith noted that the regolith is highly angular; lunar dust is sharp.
“This is not material that was broken up by being tumbled,” he said. “This is material that was broken up by being fractured by impacts.”
It’s a diverse sample. It contains basalt, breccia (material created by impacts that shatters and sometimes melts back together), and impact spheres. There was also one unusual, bright white material in the collection. It turned out to be anorthosite, which makes up about four percent of the sample.
“It represents a piece of the original crust of the Moon long since destroyed by four and a half billion years of impacts,” Smith explained. Anorthosite is an igneous rock, like basalt, that comes from the cooling of melted rock. Basalt is created when lava moves across the ground, but Smith noted that anorthosite doesn’t work that way.
“Anorthosite forms in big pools of lava, huge pools of lava, huge chambers of lava,” he said. “As these chambers of lava slowly cool over time, the anorthosite floats to the top.”
“If this was found on the Moon it must mean that at some point early in the Moon’s history it must have been almost completely molten,” Smith added. This information made scientists re-think their notions about the origins of the Moon.
“Before Apollo there was no indication that the whole, entire Moon was almost completely melted,” he said.
The leading theory about the formation of the Moon these days is that something pretty big, about the size of Mars, smacked into the early Earth, and that material flung into space by the impact eventually coalesced into the Moon. The catch is that computer simulations of this event don’t often result in a completely molten Moon. So more study is needed. The lunar samples have been under constant scrutiny for the last 50 years, and Smith says he’s interested to see what new information can be gleaned from those samples as new analytical technology is developed.
Astronomy on Tap Seattle is organized by graduate students in astronomy at the University of Washington. The next gathering is set for Wednesday, August 28, 2019 at Peddler Brewing Company in Ballard.
Leah Fulmer, who is working at the University of Washington on her Ph.D. in astronomical data science, gave a talk titled, “Data-Driven Astronomy in the 2020s and Beyond.” Fulmer explained that we’re in the midst of a “data tsunami” that’s been growing over the last three decades of astronomical surveys.
In the future this astronomical growth in data collection will continue. The Large Synoptic Survey Telescope (LSST) under construction in Chile will survey the entire night sky every few nights for ten years. It will ultimately collect an astounding 500 petabytes of data—that’s 20 terabytes every single night.
“SDSS had a total data collection of 40 terabytes,” Fulmer pointed out. “We’re going to have one SDSS every two nights in the 2020s. This is a big freaking deal.”
On top of the data, Fulmer noted that the LSST will alert its network when it finds something interesting. Given the amount of data, Fulmer said there will be ten million alerts every night, or about 232 every second.
“This is overwhelming; this is a data tsunami,” she said. “With this sort of data collection astronomers cannot do our science in the way we have up until this point.”
A new way to look at data
Up until recently astronomers would apply for telescope time, make their observations, take the data home, and analyze it. That won’t work in the era of big data for a couple of reasons. First, you can’t jam that much data onto your laptop. Second, there just aren’t enough astronomers to sort through data on objects one by one. As you might guess, we need the help of computers.
“Specifically, we need the help of machine learning,” Fulmer said. This can be both “supervised” and “unsupervised” learning. Astronomers can identify objects by their light curves, and the computers can be taught what those are. That’s supervised. In unsupervised learning, the computers can go out on their own and sort various observations into categories with similar characteristics, and we can figure out what’s in each category.
Once you figure that out, a data broker like ANTARES (the Arizona-NOAO Temporal Analysis and Response to Events System, and yes, astronomers still rule at acronyms) can let the right people know about discoveries in a timely manner.
Fulmer said it’s interesting that ANTARES will never look at the sky, just at data, and that many future astronomers may never visit a telescope, just analyze the data. Different fields can learn from each other about how to process all of this information.
Fulmer finds the era of big data exciting.
“It’s not just data-driven astronomy, it’s data-driven everything,” she said.
Astronomy with your breakfast
N. Nicole Sanchez is working on her Ph.D. in astronomy at the UW, and her research interest is in spiral galaxies like our own Milky Way and how they evolve. This, naturally, led her to think of galaxies as waffles. Thus the title of her talk, “Black Holes, Gas, and Waffles.”
Spiral galaxies form into disks, she explained, and a waffle is a disk. The galaxies have a central bulge, represented on the waffle by a big pat of butter. Marshmallows, suspended by toothpicks, represent globular clusters of stars. Red and blue sprinkles represent old red stars and young blue ones. You just have to imagine the supermassive black hole at the center of the waffle. It may be massive, but it’s super small compared to the size of the waffle.
Sanchez came up with the idea for this model while teaching at the UW in the “Protostars” summer science camp for middle school girls the last couple of years. In the waffle model, syrup represents the gas in the galaxy.
“That’s what you’re making your stars out of, so there’s going to be a lot in your disk,” Sanchez said.
In fact, her faculty advisors got wind of the waffle model and said it would need A LOT of syrup, which led to the hilarious twitter thread below. Click on it to see the academic discussion.
Also! For those of you interested in the galaxy waffles: Here’s a nice example from class!
Waffle galaxy disk
Marshmellow globular clusters
Cherry bulge/bar
Red and blue sprinkles for stars
And syrup gas
Plus a nicely labeled diagram pic.twitter.com/vw8Pnt7gZO
— Nicole “Hella Metal” Sanchez (@the_n_nicole) August 15, 2018
Sanchez admitted that her waffle galaxy may be “a bit too simplified” as a model. But the syrup is important.
“There’s actually tons of gas around really all galaxies, in what’s called the circumgalactic medium,” Sanchez said. The gas is important to the evolution of a galaxy. It feeds the black hole and helps form stars.
Sanchez studies galaxies by using cosmological hydrodynamic simulations.
“I put a bunch of particles in a box, turn on gravity, and let time happen,” she laughed. After running a simulation she looks for a galaxy similar to the Milky Way, and examines interactions between the galaxy’s supermassive black hole and the circumgalactic medium.
“The supermassive black hole is actually really vital to the evolution of the CGM because it’s moving all of this metal that’s being created in the hearts of stars in the disk of the galaxy and it’s propagating them out into the CGM,” Sanchez explained. Without a supermassive black hole, the circumgalactic medium would not look like what astronomers have observed.
David Trilling of Northern Arizona University noted that the LSST will have an 8.4-meter mirror and a camera the size of a small car.
“In terms of telescopes, this is a really, really, really big machine,” he understated. That car-sized camera will boast 3.2 billion pixels.
“You’d need 1,500 HDTV screens to look at a single LSST image,” Trilling said. LSST will scan the entire night sky every three to four nights for ten years.
“That’s about ten terabytes of data every night, which is a huge computational challenge,” he noted.
It’s an asteroid. It’s a comet. It’s complicated…
Michael Mommert of Lowell Observatory studies asteroids and comets. He said that sometimes it’s difficult to tell one from another. An asteroid can look like a comet if the asteroid is “active.” This could be because it collided with something else, or it is spinning rapidly, or it was warmed by its proximity to the Sun.
“If we can understand those active asteroids we can better understand the average asteroid,” Mommert said. “We can learn a lot about the mechanisms that are going on in asteroids from those active asteroids.”
Similarly comets can go dormant, with no tail, and look more like asteroids. As they often share similar properties, Mommert said comets and asteroids are on something of a continuum rather than being two distinct types of objects.
In his research Mommert is tracking about 20 active asteroids and 50 dormant comets. He figures he spends 30 nights per year using a telescope. He’ll be able to cut down that time tremendously with LSST; he’ll be able to find his targets and pull data collected by the telescope.
“LSST will improve our understanding of small body populations,” Mommert said. “Asteroids, comets, active asteroids, everything that is out there.”
Tales from the Outer Solar System
Kat Volk of the University of Arizona focuses her research on objects in the outer solar system. Pluto, Eris, and other far-out objects have been discovered by comparing photos of an area of sky and looking for something that moved. In fact, Pluto was the first object discovered in this way.
There are about 2,000 known objects in the Kuiper Belt. That’s about how many asteroids we knew of a century ago.
“Kuiper Belt science is a hundred years behind Asteroid Belt science because these things are just so much more difficult to find,” Volk said, because they’re far away, faint, and move slowly. “We had to wait until we had digital cameras and computers to process those images.”
Volk said we probably have discovered all of the 10-kilometer asteroids and most of the 1-kilometer ones. They’re easier to spot because they’re brighter, and there’s money for the hunt because of the potential threat asteroids pose to Earth.
“For comparison, the smallest ever observed Kuiper Belt object is 30 kilometers across, very roughly,” Volk said, adding that we only found that one because the Hubble Space Telescope was used to look for another target for the New Horizons mission after it passed Pluto.
“We’re pretty incomplete in terms of our object inventory in the outer solar system,” Volk said. She said LSST will change that.
“They expect 40,000 new Kuiper Belt ojects,” Volk said. “It’s going to be an entirely new era for the Kuiper Belt with a huge playground of new objects to look at.”
“I am realy excited to see what we’re going to find with LSST, and it’s going to completely revamp our idea of the outer solar system.”
A Crash Course in Asteroid Defense
Andy Rivkin of the Johns Hopkins University Applied Physics Laboratory said that even a 20-meter asteroid packs a wallop when it smashes into Earth. That was roughly the size of the Chelyabinsk meteor in 2013.
Doing the math tells us that there should be about 10 million objects of that size zipping around the solar system, but so far we’ve found only around 10 thousand of them. Back in 2005 Congress told NASA to find 90 percent of objects 140 meters or larger.
“LSST is going to be a critical piece in reaching this goal,” Rivkin said, “and we expect that by 2034 about 86 percent of hazardous asteroids will be found.”
So, what do we do when we spot one headed our way? Rivkin said that for really small ones, like Chelyabinsk, and really large ones, the best idea might be duck and cover. There’s not much to be done about something very large, and small ones don’t pose much of a threat. For those in between, a few options are viable. For one, we could try to deflect the asteroid with a nuclear bomb.
“A lot of people are uncomfortable with nuclear explosions in space, for good reason, and so there’s been a lot of interest in having something else that could work,” Rivkin said.
That something else is a kinetic impactor, which is a fancy way of saying we’ll just smash something into the asteroid to change its speed, and therefore its orbit. It’s a fine idea in theory, but we have no idea if it would actually work. Rivkin is involved in a project that will give it a try.
It’s called DART, which is for Double Asteroid Redirection Test. DART is on schedule to launch for the asteroid Didymos in June of 2021, and then crash into its satellite, nicknamed “Didymoon,” in October 2022. Astronomers will watch through ground-based telescopes and see what happens. Rivkin called it a dress rehearsal for the day we might have to do something about an incoming asteroid.
“A dress rehearsal for, needless to say, a performance we hope never to actually stage,” he said, “demonstrating that we could do this, allowing us to pin these computer simulations to something real, allowing us to better understand asteroidal properties, and giving us a lot of science as an ancillary benefit.”
Astronomy on Tap Seattle is organized by graduate students in astronomy at the University of Washington.
Astronomers have to date discovered more than 3,700 exoplanets—planets in orbit around stars other than our Sun. With each discovery, someone wants to know if the newly discovered planet is like Earth.
Elizabeth Tasker at Astronom on Tap
Seattle. Photo: Greg Scheiderer.
“Roughly one third of those are approximately Earth-sized, by which I mean their physical radius is less than twice ours,” Tasker said. News media often wish to leap from that to describing a planet as Earth-LIKE, but Tasker said we don’t have nearly enough information to make that sort of call. Our current methods of detecting an exoplanet can give us either its radius or its minimum mass, and a pretty good read of its distance from its host star.
“The problem is neither of those directly relates to what’s going on on the surface,” Tasker noted. Part of the challenge is what Tasker feels is the somewhat oversimplified notion of the “habitable zone” around a star, a band of distance in which liquid water—a key to life as we know it—could exist on a planet’s surface.
“Like all real-estate contracts, there is small print,” Tasker said. “Just because you’re inside the habitable zone doesn’t mean you’re an Earth-like planet. Indeed, of all the planets we’ve found in the habitable zone around their stars, there are five times as many planets that are very likely to be gas giants like Jupiter than have any kind of solid surface.”
Another misleading metric that has been used is something called the “Earth similarity index.” This method compared exoplanets to Earth on the basis of properties such as density, radius, escape velocity, and surface temperature.
“None of these four conditions actually measure surface conditions at all,” Tasker said, pointing out that the index didn’t take into account such features as plate tectonics, a planet’s seasons, it’s magnetic fields, greenhouse gases, or existence of water. We can’t observe any of those things about exoplanets yet. As an example of the flaws of the index, Venus came out at 0.9, pretty similar to Earth, which is at 1.0 on the zero-to-one scale. While Venus is about the size of Earth and is around the inner edge of the Sun’s habitable zone, its surface temperature could melt lead. Not very Earth-like, or habitable. It’s one of the reasons that the index is seldom used these days. So we don’t have much of a clue about conditions on any of the known exoplanets.
“Our next generation of telescopes is going to change that,” Tasker said. She noted that NASA’s James Webb Space Telescope is scheduled to launch next year, the ESA’s Ariel in 2026, and the UK’s Twinkle in the next year or so.
“All of these are aiming at looking at atmospheres, and these may be able to tell us what is going on on the surface, and may even give us the first sniff of life on another planet,” Tasker said. “Maybe then we’ll be able to talk seriously about Earth 2.0.”
The search for extraterrestrial life keeps getting smaller in scale. It’s difficult to discover planets around other stars, but now scientists are looking for exomoons and alien bacteria. Two University of Washington graduate students shared their work at an Astronomy on Tap Seattle gathering at Peddler Brewing Company in Ballard last week.
To date more than 3,500 exoplanets have been discovered in orbit around stars other than our Sun, but we haven’t seen an exomoon orbiting any of those planets. Tyler Gordon, a second year grad student in astronomy and astrobiology at UW, thinks it’s only a matter of time before we do.
“We have every reason to expect that there are a lot of moons out there in the universe, probably many more than there are exoplanets,” Gordon said. Thinking about our own solar system, he pointed out that there are 19 moons that are big enough to be rounded by their own gravity, which is more than twice as many such moons as there are planets.
Despite the fact that no exomoons have yet been found, Gordon said there are three good reasons to look for them:
They might be habitable
The presence or absence of a moon can give a clue about how a planet formed
A moon can be a factor in a planet’s habitability
There are two reasons for that third point. Moons can raise tides, and some scientists think that tides battering the shore on early Earth delivered nutrients and created places for life to develop. In addition, moons can influence a planet’s orbital characteristics, especially obliquity, and help stabilize oscillations of its rotational axis.
“An exomoon can keep a planet from tumbling back and forth onto its side and can insulate it from having really extreme changes in seasons, which is something that we think could be very bad for life,” Gordon said.
Where are they?
It’s been hard enough to identify exoplanets, and there’s an obvious challenge in hunting for exomoons.
“Exomoons are probably really small, and small is a problem because small things are really hard to see,” Gordon noted.
Just how small are moons? Gordon explained that observation and modeling have found that the mass of a planet’s satellites generally scales with the mass of the planet itself. For any given planet, “We expect that the total mass of its satellites adds up to between one ten-thousandth and two ten-thousandths of the mass of their host,” Gordon said.
Thus to find an exomoon as big as Earth—something we could actually see—its host planet would have to be about 30 times the mass of Jupiter. Something that big probably wouldn’t be a planet; it would more likely be a brown dwarf.
Finding an exomoon
Most of the exoplanets discovered to date have been spotted because they cause a dip in the light we see coming from their star when they transit in front of it. An exomoon would do the same thing, but Gordon said there are a couple of challenges. Since the exomoon would be far smaller than the planet, so would the dip it would cause. Plus, sometimes the exomoon will be ahead of, behind, or blocked by the planet, making patterns more difficult to tease out of the data.
Gordon noted that a team from Columbia University recently tried to do that by looking at a ton of Kepler data and searching for scattering called the “orbital sampling effect.” In all of the data they found exactly one potential signal for an exomoon; it’s in orbit around the planet Kepler-1625b. This is a big planet, about ten times the mass of Jupiter, and the moon—Kepler-1625bi—is about the size of Neptune, which is way bigger than would be expected according to the scaling rule. Gordon said that raised a lot of questions.
“Is Kepler-1625b even a planet if it’s that’s big? Is the moon actually even there at all?” he asked. “And if it is there, how can such a large moon form?”
The Columbia team used the Hubble Space Telescope to look at the system back in October, but analysis of the data and any answers to those questions have yet to be published.
Gordon said that the James Webb Space Telescope will be a big help to exomoon hunters. While Kepler looked in the visual, JWST is equipped for other wavelengths.
“By using JWST’s ability to see in different parts of the electromagnetic spectrum we may be able to disentangle the transit of an exomoon from stellar variability that could obscure that transit,” Gordon said.
Space bacteria
Max Showalter is looking for stuff way smaller than exomoons. He’d like to spot interplanetary bacteria.
Showalter, a Ph.D. student in oceanography at the UW, gave a talk titled, “Looking for Life When the Trail Goes Cold.” He noted that the hunt for biosignatures is at the heart of the search for life. Biosignatures can be chemical, say oxygen in an atmosphere. They can be structures, such as fossils. They could be biological molecues like amino acids or nucleotides.
“They tell us that either life has been there in the past, or life is there now, or life could be there in the future,” Showalter said. “We want lots of biosignatures all telling us the same thing in order for us to decide that there’s life.”
Showalter would add another biosignature to the list: movement. After all, there’s no better sign of life than if something comes up and waves at you. Still, when you’re looking for microbial life, the tough questions are whether bacteria swim in space, and how we’ll see them if they do.
“It’s hard enough to see microbes on Earth, let alone millions of miles away,” Showalter noted. His research specialty is studying things that live in sea ice. When salt water freezes, the salt can either fall out or get stuck inside the ice. If it’s inside, the salt gets concentrated and melts pockets of ice, creating what are called brine pores.
“These brine pores are great because they make a really good habitat for a lot of things to live inside the ice,” Showalter said.
Ice-beings on Earth
Showalter has looked at bacteria from Arctic sea-ice on site with a microscope called SHAMU, which stands for “Submersible Holographic Astrobiology Microscope with Ultra-resolution.” SHAMU works on principles of holography. A laser in a box is split into two beams. One beam goes through the brine sample, the other goes straight to a camera. The waves of light interfere with each other, and computer analysis can create a hologram: “A 3-D image of a tube of liquid where you can see bacteria swimming,” Showalter said. (Read a longer article about SHAMU from a talk Showalter gave at Town Hall Seattle in 2016.)
The application for SHAMU in the search for life is at places like Saturn’s moon Enceladus and Jupiter’s moon Europa, both of which have salt water oceans under thick crusts of ice. Some of this salt water shoots out of geysers on the moons and into space.
“Which presents a really incredible opportunity for us as astrobiologists—or astronomers if you’re one of those people—to be able to sample that ocean without having to drill through eight kilometers of ice!” Showalter said.
An upcoming NASA mission called Europa Clipper will take a shot at that. The spacecraft is presently scheduled for launch some time between 2022 and 2025. SHAMU isn’t going, and none of the instruments selected for the mission will be looking for bacterial motility, but Showalter holds out hope that motility will prove to be a useful biosignature in the future.
He said he doubts that Europa Clipper will find life, but expects it will come across some tantalizing clues.
One of the cool things about the Astronomy on Tap Seattle series of talks in pubs is access to scientists who are working on headline news. It happened at their October gathering at Peddler Brewing Company in Ballard. Jennifer Sobeck, a stellar astrophysicist in the Department of Astronomy at the University of Washington, was all set to give a talk titled, “A Hitchhiker’s Guide to the Galaxy: Bumming Around the Milky Way.” But a few days before the talk the news hit that LIGO and others had detected gravitational waves generated by merging neutron stars. Neutron stars are Sobeck’s thing, so the script went out the window and we learned about what happened.
Sobeck noted that neutron stars are what’s left behind when high-mass stars—around four to eight times the mass of the Sun—blow up in a supernova. Neutron stars are incredibly dense; the mass of the Sun packed into something 12 miles across. They have a crust, though light still gets through.
“Inside is just basically a soup,” Sobeck said. “It’s a hot mess.”
Everything inside is so compressed that scientists call it “degenerate.”
“There are no more atoms, there are no more molecules, those are all blown apart,” Sobeck explained. “It’s just like a soup of neutrons; there are just tons of neutrons, and the really cool thing is down in the center, they think the pressures are so high that you actually might get quarks.”
August discovery
Scientists knew they had detected a neutron star merger rather than the sort of black-hole mergers previously spotted by LIGO because the signals are different. The interesting thing about the detection of two neutron stars merging is that we could see it visually because the event created a kilonova, like a supernova, but smaller.
“It’s a little bit less on the explosion scale,” Sobeck said. “Kilonova means that you’re able to have electromagnetic radiation across the spectrum that a whole bunch of facilites were able to monitor.”
So when LIGO and VIRGO detected the gravitational wave, with the help of the Fermi gamma ray space telescope and the ESA’s Integral gamma-ray observatory they they were able to narrow down the location of the event and tell others to look there. When the optical observations came in, the kilanova was spotted in the galaxy NGC 4993.
“This has never been done before,” Sobeck noted. The detection occurred in mid-August of this year, and by the end of the month the visual was gone.
“This kilonova explostion lasted only for a period of only 15 days,” Sobeck said.
Observations were made not just in the visual, but across the spectrum from gamma rays to radio, and more than a dozen observatories were involved in the analysis.
“You’re getting a different piece of information from all of these parts of the spectrum,” Sobeck noted. “They all helped fill in that puzzle.”
The story in the media
Sobeck said the press went a little overboard with headlines such as collision “creates gold” (CNN) and “Universe-shaking announcement” (New York Times), yet it’s true that the kilonova made some gold. Sobeck noted that hydrogen, helium, and a bit of lithium came from the Big Bang, but the rest of the elements were made in stars. But stars can only fuse elements as heavy as iron. To get the really heavy stuff called lanthanides you need a kilanova. The emitted light tells you what’s there. If you see blue light after a kilonova, that means there’s a high concentration of silver, cadmium, and tin. If the light is more red, then platinum, gold, mercury, or lead is present.
“This particular event went from blue very, very, quickly to red, and it stayed red most of the time,” Sobeck said. “Hence, we’ve got a bunch of gold on our hands.”
“We found out that neutron-star mergers do make elements,” she said. “We were right, so huzzah!”
All kinds of galaxies
Grace Telford, a graduate student studying astronomy and data science at the UW, stuck with her original topic of “A Whirlwind Tour of Galaxies: the Tiny, the Gigantic, and Everything in Between” for the October Astronomy on Tap. She noted that there are several ways to classify galaxies:
Stellar mass or brightness
Shape
Star formation rate
Nuclear activity
Stellar mass or brightness
This is pretty straightforward.
“Basically the more stars a galaxy has, the brighter it is,” Telford noted. There’s quite a range of sizes. The Milky Way is a pretty common-sized galaxy, and it’s hard to make them bigger. The largest are around 10 times the size of the Milky Way.” Smaller galaxies are plentiful.
“A dwarf galaxy is something that is at least a hundred times less massive than our Milky Way,” Telford said, and they can go a lot smaller.
Way out at the small end of the chart are ultra faint dwarf galaxies, which can’t really be seen because they’re too faint. They can’t be detected at long distances.
A recently discovered type is called an ultra diffuse galaxy. This may be the same size as the Milky Way but have 100 times fewer stars, all held together by dark matter.
“This is an open area of research,” Telford said. “It’s hard to explain how to form these wierdo galaxies that are not very massive at all, but huge.”
Shape
The three main shapes of galaxies are elliptical, spiral, and irregular. Spirals may come with a large central bulge or a bar. Irregular galaxies tend to be small.
Star formation rate
It’s in star formation rate that galaxies really differentiate themselves, Telford said. Galaxies that emit a lot of blue light have lots of young stars and new star formation. Galaxies that look red are “quenched.” Their stars are older, and there’s little new star formation.
In between red and blue is the “green valley” of galaxies. They don’t actually emit green light, but they’re in transition from blue to red.
An interesting type is the “starburst” galaxy. These are galaxies that somehow stumble into a source of gas that wasn’t available to them before.
“They have the ability to form stars at a very high rate relative to the normal amount of star formation for a galaxy of its size,” Telford explained. “As a result, you have a lot of these massive young stars that are dying and exploding as supernovae and injecting a lot of energy into the gas.”
These objects are short-lived, they exhaust their gas in a hurry, at least in astronomical terms—in between 100 million years and a billion years.
Nuclear activity
Most galaxies have supermassive black holes, which can create jets of energy.
“Sometimes these black holes eat a lot of gas really quickly and then they blow out a whole bunch of energy,” Telford explained. These jets are nuclear activity. Galaxies with active galactic nuclei are most typically found in the green valley, though they’re in other types as well.
Telford gave a plug for Galaxy Zoo, where you can go looking for these differing types of galaxies and actually participate in citizen science.
The topic line for last week’s gathering of Astronomy on Tap Seattle was What the Hell is Polarimetry?, and it seemed that a significant portion of the audience at Peddler Brewing Company in Ballard shared the question.
UW postdocs Jamie Lomax and Kim Bott explained that when light starts from its source the oscillation of its wave—its “wiggle”—goes in all directions until an interaction with something makes it polarized.
“That just means that it’s wiggling in one direction,” Lomax noted. “There’s a preferred plane for that wiggle to happen in, and in polarimetry what we’re doing is measuring that preferred plane and we’re looking for light that has been polarized.”
“It can help you figure out the shape of things without having to resolve the object,” Bott added.
Polarimetry and massive stars
Jamie Lomax
Lomax studies massive stars and has found use for polarimetry in her work. She gave a talk titled, “Seeing Invisible Circumstellar Structures.”
“The holy grail for us in massive star research is to be able to take a massive star at the beginning of its lifetime, figure out how massive it is,” Lomax said, “and map out what its life is going to look like and figure out what supernova it’s going to end its life as.”
“It turns out that is really hard, and it’s complicated by the fact that most massive stars are probably in binary systems,” she added. Since about two-thirds of massive stars are part of a binary system, one might expect that two-thirds of core-collapse supernovae would be from such systems.
“There’s a problem, and that is we’ve only seen maybe two or three core-collapse supernovae where we have evidence that suggests that it’s come from a binary star,” Lomax said.
Part of the problem, she said, is that we don’t yet know enough about the evolution of binary star systems.
“We can try to hammer out the details of how that mass is transferring between the two stars and when the system is losing material to try to figure out how that effects its future evolution,” Lomax said. “Once we start answering questions like that we can start to tease out why we aren’t seeing all of these binary supernovae we think we should be seeing.”
Lomax talked about the star Beta Lyrae, a binary system. The primary star in the system is losing mass that gets gobbled up by the secondary. This transfer of mass also forms a thick accretion disk of gas around the secondary—so thick light from the actual star can’t get through. There’s also evidence that there are jets shooting out of the system, but we don’t know where they are.
“These are all features that we can’t see very well,” Lomax said. “We can’t see the mass transfer stream between the two stars, we can’t see the jets.”
Here’s where polarimetry comes in. If a star is surrounded by a cloud of gas or dust that is circularly symmetrical, when the starlight interacts with that material the light becomes polarized, and the wiggles line up tangentially with the edge of the disk. If the cloud is elongated in some way, the wiggles form in a “preferred” direction.
“That preferred wiggle direction is 90 degrees from the direction of the elongation of the disk, so you can back out geometric information pretty quickly,” Lomax said. “Just by looking at how the light is wiggling I can tell you how the disc is oriented on the sky.”
Lomax figures that if you don’t do polarimetry you’re throwing out free information.
“You can see invisible things—to you—and that gives you extra information about what’s going on in different systems.”
Exoplanets and aliens
Bott’s talk was titled “The Polarizing Topics of Aliens and Habitable Planets.” She studies exoplanets and said polarimetry comes in handy.
“Stars don’t produce polarized light, which is really great if you’re trying to look at something dim like a planet,” she noted. The polarimeter will simply block out the starlight. There are then a number of things that might be spotted on the planet:
Glint from an ocean
Rayleigh scattering
Clouds and hazes
Rainbows
Biosignatures of gases in an atmosphere
Chiromolecules
Kim Bott
These can help astronomers characterize a planet, judge its potential habitability, and even determine if life might already be flourishing there.
Bott said that polarimeters that are sensitive enough to study planets are a recent advance, and they’re studying big, bright planets to get the hang of it. Looking for rainbows can be revealing about liquids in the atmosphere of a planet.
“The light will bend in the droplets at a slightly different angle depending what the droplet is made out of,” Bott said, so they can tell whether its water, methane, or sulfuric acid.
“We’re trying to create these really robust models that will take into consideration polarized light from Rayleigh scattering in the atmosphere as well as from rainbows,” Bott said, “and if you have a planet where you can see the surface you’d be able to see the signature from glint as well.”
Since different substances bend light at different angles, we can also learn a lot by watching closely as planets move through their phases as they orbit their host stars.
“On Earth we have light going from air and bouncing off of H2O water,” Bott said. “That’s going to produce a maximum in polarized light at a different angle than on, say, Titan, where you have light going from a methane atmosphere and then bouncing off of a hydrocarbon ocean.”
“We can actually, in theory, tell what the ocean and atmosphere are made out of by looking at where, exactly, in the orbit we see this glint,” Bott explained.
As for aliens, life requires more complex molecules, chiromolecules, that are “wound” in a certain direction, like our own DNA. Such molecules would produce circularly polarized light, which if detected could be a sign that such molecules exist on the planet.
Often when an exoplanet is discovered the first question asked by the mainstream media is whether the new planet is “Earth-like.” In truth we know little about these far-away planets other than their mass or size, and whether they orbit within the habitable zone of their host star. Scientists are using PCA and SAMURAI to learn more about exoplanets, and LUVOIR may ultimately help us get a much better look at these distant worlds.
Lupita Tovar spoke about mapping
exoplanets at Astronomy on Tap
Seattle August 23, 2017.
(Photo: Greg Scheiderer)
Big is the operative word for LUVOIR. Astronomers love aperture for their telescopes, and LUVOIR would dwarf any space telescope to date. The Hubble Space Telescope has a 2.4-meter mirror, and the James Webb Space Telescope, scheduled for launch next year, will be 6.5 meters. LUVOIR would nearly double that; Tovar said it is proposed right now to have a 12-meter mirror. It would also be equipped with a coronagraph which would block the light of a host star. Much as Venus and Mars were visible in the daytime during last month’s total solar eclipse, blocking starlight would allow us to see much dimmer objects nearby.
“The coronagraph will allow us to see those close-in planets, like Venus, and allow us to study those planets,” Tovar said. LUVOIR would be a powerful instrument. It could see Venus, Earth, and Jupiter from a distance of ten parsecs, or about 33 light years.
Fortunately, astronomers don’t have to wait for LUVOIR to make progress on mapping exoplanets. Tovar said that today they’re using PCA—Principal Component Analysis—to get a better idea about an exoplanet’s surface.
“We use PCA to extract how many components are there,” Tovar explained. “Is it just one, solid icy body? Are there two different types of surfaces sitting on that planet? Are there three? Are there more? PCA allows us to extract that information.”
Call in the SAMURAI
Once they know how many surface types there are, astronomers can then use SAMURAI—Surface Albedo Mapping Using RotAtional Inversion—to figure out just what those surfaces are. Tovar said it’s like looking at a beach ball as it is batted around. As the ball spins, different colors face the observer. SAMURAI uses algorithms to determine the composition of each surface type. For example, land reflects more light than ocean does, but an ocean’s reflection will spike when it’s near the edge of the exoplanet, from our view, because of the glint of light from the host star.
LUVOIR is just a glint in the eyes of astronomers now, but it along with PCA and SAMURAI could give us a much better idea about the makeup of exoplanets.
“Combined together, all of these three components will help you create a map,” Tovar said.
Is Tatooine out there?
Star Wars fans often speculate about the existence of planets like Luke Skywalker’s home world Tatooine, which has two suns. So far we know of a dozen exoplanets in orbit around binary star systems. Diana Windemuth, also a Ph.D. student in astronomy and astrobiology at UW, studies these sorts of systems and gave a talk titled, “By the Light of Two Suns” at Astronomy on Tap Seattle.
Diana Windemuth discussed exoplanets
orbiting binary star systems at AoT
Seattle. (Photo: Greg Scheiderer)
“Our Sun is a bit of a weirdo in that it does not have a companion,” Windemuth said, explaining that about half of stars like the Sun have one. The more massive a primary star is, the more likely it is to have a companion, she said. Further, there are two types of stable orbits a planet in a binary star system can have. In an S-type orbit the planet will go around just one of the stars; it will be either a circumprimary or circumsecondary orbit. In the P-type, the exoplanet orbits both stars.
“A circumbinary planet goes around in a wider orbit around an inner, closer-in binary,” Windemuth explained. She said it is harder to find these sorts of systems using Kepler’s transit method because throwing in a third body complicates things. Kepler measures the overall light from a system, and the amount of light we see changes not only when the planet transits, but when the stars eclipse each other.
“These are called eclipsing binaries because they go around one another,” Windemuth said. Exoplanets are confirmed when dips in the light during transits happen at regular intervals. Usually a computer picks that out of the data, but it doesn’t work so well on binary systems.
It’s a trick!
“It turns out its difficult to train a computer to do that because of what we call the geometric effect,” Windemuth said. Because the stars move with respect to each other in binary systems, the period of transits can appear to vary because of differing distances the light travels to reach us. Gravitational interactions in the system can also create wobble and change the perceived period of transits.
“Even though the period of your planet might be the same, the transits will occur at different times,” Windemuth noted.
It’s probably because of these challenges that we’ve only discovered a handful of circumbinary planets so far, Windemuth said, and none of them are candidates to be the real-life Tatooine.
“No terrestrial circumbinary planets have been found yet,” she said. That could be because they’re too hard to find, or maybe planets with short periods are destroyed when they orbit too close to the binary stars.
“It’s probably because our detection algorithms are not good enough yet,” Windemuth concluded.
The universe is full of mysteries; that’s one of the reasons that astronomy is so interesting! We dug into a couple of puzzling phenomena at the most recent gathering of Astronomy on Tap Seattle at Peddler Brewing Company in Ballard. The session was dubbed “CSI: Universe,” and Brett Morris, one of the co-hosts of Astronomy on Tap Seattle and a Ph.D. candidate at the University of Washington, gave a talk about the star KIC 8462852, more commonly called Tabetha Boyajian’s star, thank goodness. His talk was titled, “The Weirdest Star Gets Weirder.”
You helped
Citizen scientists were the first to notice that there was something odd about Tabby’s Star. The Kepler Space Telescope was searching for exoplanets by watching for slight but regular dips in a stars brightness, a possible indication of a planet in orbit around a distant star. Morris noted that it can be difficult to write a computer algorithm to filter out noise in the data, so they enlisted the help of the public through the website PlanetHunters.org.
Brett Morris (Photo: Greg Scheiderer)
“What you can do on this website is help scientists look for things that are weird,” Morris said. People identify objects that don’t look right, then professional astronomers check them out. “Through this process they found a whole bunch of stars that misbehave.”
One of them was Boyajian’s.
“If we look at its colors, if we look at its spectrum, it behaves like all the other F-stars,” Morris said, “and so we were a little bit puzzled when we started looking at data.”
There were dips in light from Tabby’s Star, all right. There were smaller dips early in the mission that never really matched up. Then in March 2011 there was a huge dip of 15 percent of the star’s light, and it lasted for days, not hours as most transits do. Then in February 2013 there was an even bigger reduction in brightness of 20 percent. Nobody has come up with a plausible explanation for this.
“Whatever this is, this thing’s big,” Morris said.
No easy answer
An astounding array of possible explanations have been thrown out there. Examples include an object like Saturn with rings that could cause variations in the light curve, a passing comet, debris from a huge planetary impact like the one thought to have formed our Moon, and Tabby’s Star’s indigestion from having just swallowed a whole planet. The one in vogue at present is that a family of 10 to 20 comets, all giving off material, are creating these odd light curves. Morris doesn’t quite buy this one, either.
“The more bodies that you imagine being there, the easier it is to fit a light curve,” he said. “If you just keep adding new parameters into your model, eventually it will fit.”
“If you invoke weirdly shaped objects, you can fit it perfectly,” Morris added. “If you invoke the kinds of objects that we expect are most likely, it’s a lot harder. We really don’t know what this star is doing.”
Some have wondered if something between us and Tabby’s Star, maybe interstellar gas or dust, caused the strange light curves. Morris himself investigated this one. Back in May he got a Tweet—he said this is mostly how astronomers communicate these days!—noting that Tabby’s Star’s brightness was changing. He used the Apache Point Observatory to look for signs of absorption from interstellar gas or dust. But the spectra didn’t change even though the star was changing.
“We’re slowly ruling things out,” Morris said. “It’s not something in our solar system, it’s not something between us and the star; it’s got to be something near the star, but we don’t know what near the star could be doing this.”
As for wild speculation that the strange light curves could be caused by a Dyson Sphere or other “alien megastructure”:
“Extraordinary claims require extraordinary evidence, and I do not have any evidence to suggest that we can make a claim as extraordinary as that,” Morris said. He and a team of undergraduates at the University of Washington continue to work on the puzzle.
Coroner for the Stars
The second talk of CSI: Universe came from Prof. Melissa Graham of the UW, who does work on supernovae. These mark the death of a star, and Graham’s job is to figure out whodunnit.
Melissa Graham (Photo: Greg Scheiderer)
Graham pointed out that a star is considered alive if it’s in hydrostatic equilibrium; that is, when atomic fusion in the star’s core supports the star by counteracting gravity. Sometimes the death of a star is from natural causes. A typical star will fuse hydrogen and helium into carbon, then gradually fuses neon, oxygen, and heavier elements until eventually a core of iron forms. Graham said this means trouble, because fusing iron into something heavier is not exothermic; it doesn’t release energy.
“If you end up with a core of iron, your hydrostatic equilibrium suffers because you are losing out on that fusion in the core,” she said. “The core collapses because it can’t support itself anymore, the outer layers fall onto the inner layers, and you end up with a supernova explosion.”
Material blows away and leaves neutron star behind.
“That’s death by natural causes,” Graham said.
Type 1a supernovae are more interesting to stellar criminologists. These involve a white dwarf star, which is the remnant of a smaller star that doesn’t have enough mass to fuse carbon and oxygen into anything heavier.
“The carbon and oxygen core shrinks under its own self-gravity, and the outer layers are lost, which causes a really pretty planetary nebula,” Graham said. “The star is now supported by electron degeneracy pressure.”
This means the star isn’t alive because it’s not fusing elements.
“It’s more of a zombie star,” Graham said. “It’s died once and continues to live.”
The usual suspects
It’s a suspicious death when you see one of these explode. Graham rounded up the usual suspects: It could be a binary companion, such as a red giant or a sun-like star or another white dwarf. Sometimes it could be a pair of white dwarfs with a third companion star. A type 1a supernova also might from from a white dwarf’s impact with a primordial black hole or comet.
One way to figure this out is to simply look at the scene of the crime.
“Once this white dwarf star explodes, the other companion star would still be there,” Graham said. A companion would heat up and get brighter, so it might be detectable. Interstellar dust and gas may also light up from the energy of a supernova. Looking back at the scene later might detect such material that is at significant distance from the event. Graham is using the Hubble Space Telescope to check to find out if this is happening. She’s also looking forward to the completion of the Large Synoptic Survey Telescope, which is expected to find some ten million supernovae over its 10-year mission. With so many new examples we will, “really start to understand how these carbon-oxygen white dwarfs die,” Graham said.
