Making beer and weighing stars

Science these days is often all about interdisciplinary work. It’s seldom just biology or just geology, and so it wasn’t surprising that the most recent gathering of Astronomy on Tap Seattle had a heavy dose of chemistry. It was for a good cause, though, as Trevor Dorn-Wallenstein, a second-year graduate student in the University of Washington Astronomy Department, gave a talk titled “An Unbeerlievable Tale” explaining how the universe made us beer, and a glass to put it into. The event happened July 26 at Peddler Brewing Company in Ballard.
It turns out you only need five elements for beer:

• hydrogen
• nitrogen
• carbon
• oxygen
• phosphorous

Trevor Dorn-Wallenstein talks about
celestial beermaking at Astronomy
on Tap Seattle July 26, 2017 at Peddler
Brewing Company in Ballard.
(Photo: Greg Scheiderer)

We had the hydrogen about a millionth of a second after the Big Bang.

“It’s not until 10 seconds after the big bang that we can smoosh a proton and a neutron together and have deuterium and have that deuterium last,” Dorn-Wallenstein said. “Once we have that deuterium though, we’re off to the races.”

If you add a proton to the deuterium you make helium 3, or add a neutron and make tritium. Add the missing nucleon to either and you’ve got helium 4. It’s not in beer, but we’ll need it later. Much later. We have to wait about 1.5 million years, until stars start to form and start fusing new elements. Stars about two times the mass of our Sun can fuse hydrogen into helium, then toward the end of their life cylcles do what Dorn-Wallenstein called the “triple alpha reaction.” They smash three helium atoms into carbon, and add another helium nucleus to make oxygen. When the star reaches its red giant phase these elements blow off with the stellar wind.

“We’ve polluted the interstellar medium with hydrogen, with carbon, with oxygen,” Dorn-Wallenstein said, “three of the things we need to make beer.”

Higher-mass stars, say ten times the mass of the Sun, can fuse things such as neon, titanium, silicon, sulfur, magnesium, aluminum, and calcium.

“It can unlock all of these additional stages of nuclear fusion,” Dorn-Wallenstein said.

Nickel beer night

The process leaves behind a stellar core of nickel 56 which decays into iron 56.

“Iron 56 is the end of the line for a star,” Dorn-Wallenstein explained. “There is no physical way to get energy out of an iron 56 nucleus. You cant fuse it with something else, you can’t fission it and turn it into two more things, you get nothing out of this nucleus. That’s a problem for a star.”

The outer part of the star collapses onto the core and explodes into supernova, blasting all of the elements it has made out into the interstellar medium.

“The environment around this supernova explosion is so energetic that you can make pretty much anything you want,” Dorn-Wallenstein said. “Pick any element in the periodic table that’s heavier than iron—it’s probably made in a supernova.”

Nitrogen is conspicuously missing from the list, and it is kind of hard to make. Dorn-Wallenstein said we get a little bit, but not enough, from supernovae or at the end of a smaller star’s life.

“The only way to produce enough nitrogen is via this thing called the carbon-nitrogen-oxygen, or CNO, cycle,” he said, explaining that this is how stars produce helium from hydrogen. Since nitrogen takes longer, it builds up in stars. In the universe at large there are about four or five carbon atoms for every nitrogen atom, but in a star that’s doing the CNO cycle there are more than a hundred times more nitrogen atoms than carbon.

“Via this process of converting hydrogen into helium, we actually make nitrogen as a by-product,” Dorn-Wallenstein said.

The beer glass

We’ve got the ingredients for beer. Where do we put it?

“It turns out the most complicated thing that goes into a beer is the glass itself,” Dorn-Wallenstein said, noting that your mug is mostly silicon dioxide, with a bit of sodium oxide, aluminum oxide, calcium oxide, and trace amounts of potassium, magnesium, iron, titanium, and sulfur. All of that stuff came out of a supernovae.

We have all we need for beer. Now we just need a planet to form, simple life forms like yeast to emerge, wheat and hops to grow, and someone to mix it all into a barrel and let it sit for a while.

“Look at that; we’ve made beer,” Dorn-Wallenstein concluded.

Weighing stars

The second talk of the evening at Astronomy on Tap Seattle was given by Dr. Meredith Rawls, who spoke about “Weighing Stars with Starquakes.” Rawls employs asteroseismology—your word of the day!—to figure out the mass of stars.

Dr. Meredith Rawls discussed a new method for determining
the masses of stars at Astronomy on Tap Seattle.
(Photo: Greg Scheiderer)

Rawls noted that one way to calculate the mass of a star is to observe binary systems. We can measure the blockage of light as the stars orbit each other, and the Doppler shift that occurs when they do. Combine those two measurements and you get a reliable measure of the stars’ masses.

The drawbacks, according to Rawls, are that not all stars are part of binary systems, and that this method is slow and uses a lot of limited telescope time. Rawls gets around this by using asteroseismology, measuring the oscillations, or starquakes, that occur in a star’s interior. They actually ring like a bell, though you can’t hear it because space is a vacuum, and the frequency is too low in any case. Like a bell, the more massive the star, the lower the frequency of the oscillation. You can’t see the oscillations because they’re inside the star, but they change the star’s brightness. This is something that can be observed, and astronomers chart brightness changes against the frequencies of the starquakes and see how they line up with other properties of the star.

“You fit a bunch of curves to a bunch of wiggles and you try to convince yourself you’re not making it up,” Rawls quipped. The method can give clues about a star’s surface gravity, density, and temperature, and with gravity and density you can calculate mass.

Does it really work?

Rawls said they like to study red giant stars for a couple of reasons: that’s the eventual state of our Sun, and red giants brighter and easier to see. After figuring masses of many red giants with asteroseismology, they went back and calculated them again using the binary method. Then they compared the two.

“Oh, crap!” was Rawls’s reaction upon seeing how they matched up. “It’s not one-to-one. I broke science!”

In fact, the masses calculated through asteroseismology differed from those returned by the binary method by about 16 percent, on average. It turns out that big, red giant stars are not quite so simply just huge versions of our Sun.

“They have their own weird convection stuff going on,” Rawls explained. “There’s different stuff happening in different layers of the star that isn’t quite the same as what happens inside our Sun, and it’s just complicated enough that you can’t compare them one to one, even though it would be super handy if you could.”

What do they do to reconcile the differences between the two methods?

“We have to apply empirical corrections in order to get accurate masses,” Rawls explained. In other words, “We have to fudge it a little bit! But it’s consistent. It’s fine, it’s fine. Totally works. Not a problem. Don’t worry about it,” she laughed, adding that asteroseismology works just great for smaller stars like the Sun.

“It’s actually really useful, even though sometimes it doesn’t always work perfectly, because you can measure a lot of stars’ masses really fast,” she concluded.

Astronomy on Tap Seattle is organized by graduate students in astronomy from the University of Washington.



Videos of the July talks:

Solar eclipses and the stature of science

A total solar eclipse that crossed the American West in 1878 helped ignite a great boom in science in the United States. David Baron is hoping that, in an era in which people have to march in the streets in support of science, the total solar eclipse that will cross the nation next month will be similarly inspirational. Baron, a former science editor for National Public Radio, is the author of American Eclipse: A Nation’s Epic Race to Catch the Shadow of the Moon and Win the Glory of the World (Liveright, 2017). He spoke about the book last week at the Pacific Science Center, part of the center’s Science in the City lecture series.

Baron saw his first total solar eclipse from Aruba in 1998.

“I was just dumbfounded,” he said at the sight of the eclipse, which revealed stars in the daytime and Jupiter, Mercury, and Venus. “There, among the planets was this thing; this glorious, bewildering thing. It looked liked a wreath woven from silvery thread and it just hung out there in space, shimmering.”

It was the Sun’s corona, and Baron said the photos you’ve seen don’t do it justice. Soon, the eclipse was over.

“The world returned to normal, but I had changed,” Baron said. “That’s how I became an eclipse chaser.”

He said he decided that day, on the beach in Aruba, that he wanted to write a book about solar eclipses. He also figured 2017 would be the year to release it, with public interest in solar eclipses likely to be at its apex because of this year’s eclipse. So his book has been 19 years in the making. He said the work started in earnest about seven years ago, when he went researching for interesting eclipse stories to tell.

The American eclipse of 1878

Baron came upon a historical marker next to Battle Lake in the Wyoming Sierras, which claims that Thomas Edison came up with the idea to use bamboo as a filament for an electric light bulb while fishing at the lake in 1878. Baron found no evidence that this was actually true, but Edison was involved in eclipse watching in Wyoming that summer, for the total solar eclipse of July 29, 1878. The eclipse ran from Montana south down across the American frontier through Texas. At the time, Baron noted, Europeans were the clear leaders in eclipse science.

“Here was America’s chance to shine—or an opportunity to slip up and embarrass ourselves—but if all went well we would show the rest of the world what we were capable of as a scientific nation,” Baron said, “and so the eclipse was a big, national undertaking.” The eclipse and the expeditions to observe it received in-depth coverage in the newspapers.

Edison was among a group that went to Rawlins, Wyoming to view the eclipse. The group included Norman Lockyer, who had discovered helium on the Sun and founded the journal Nature; and James Craig Watson, an astronomer at the University of Michigan, who was in search of the hypothetical planet Vulcan that could explain orbital anomalies of Mercury.

Author David Baron spoke about his book
American Eclipse on July 19, 2017
at the Pacific Science Center.
(Photo: Greg Scheiderer)

Also out west was Maria Mitchell, professor and director of the Vassar College Observatory, who brought a group of Vassar students to Denver to show that women could do science, too. For Edison’s part, he was anxious to test an invention he called the tasimeter, intended to detect minuscule changes in temperature. Astronomers were interested in the device, which might reveal if the Sun’s corona gave off heat.

“These three main characters of mine had a lot on the line,” Baron said, and on the day of the eclipse they declared great success and the press was highly positive, though neither Edison, Watson, nor Mitchell really achieved their set goals.

“Maria Mitchell did help open the doors of science and higher education to women, but it’s not like male scientists suddenly embraced their female counterparts,” Baron noted. “It was the beginning of a long, hard, continuing struggle.”

Watson didn’t find Vulcan, of course; the precession of Mercury’s orbit was explained later through Einstein’s general relativity. Edison’s tasimeter never lived up to the hype. He did head home and start work on the light bulb, though not in the way the Historical Landmark Commission of Wyoming would have you believe.

“The eclipse of 1878 did not illuminate America in the way the historical marker claims,” Baron said. “However it did enlighten America, helping to push this upstart nation toward what it soon would become—the undeniable global superpower in science, a country that would, in this intellectual realm, eclipse the world.”

Learning from history

Baron sees an interesting parallel with next month’s total solar eclipse.

“Once again the Moon’s shadow will visit us at an interesting time in our intellectual development,” he noted. “Today the issue isn’t whether America can rise up and take on the world in science, the question is whether America can maintain its global lead.”

It will undoubtedly be the most widely viewed total solar eclipse in human history. We’ll see whether it has the power to change hearts, minds, and the course of history.

---

You can purchase American Eclipse though the link above or by clicking the image of the book cover. Purchases made through links on Seattle Astronomy support our ability to bring you interesting astronomy stories. Thank you!

CSI Universe: Unraveling the mysteries of Tabby's Star and supernovae

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.