Cannibal galaxies and asteroid mining

Our galaxy is a cannibal, and we have quite an appetite for resources in our own little corner of the Milky Way, too. That’s what we learned at the latest Astronomy On Tap event in Seattle, held last week at Bad Jimmy’s Brewing Company in Ballard.

John Lurie talked about the cannibal
Milky Way galaxy at Astronomy on
Tap Seattle. Photo: Greg Scheiderer.

John Lurie, a graduate student in astronomy at the University of Washington who studies the structure of the Milky Way, started his talk with a bit of history. For millennia, up until recently when light pollution made the Milky Way invisible to a great many of us, people saw it and made up stories about what it was. To Lurie’s mind, some of the violent images of Greek mythology seem fitting.

“Our Galaxy is actually a cannibal, and it likes to eat other galaxies,” he said. “Not only that, but the entrails of its victims are strewn across the heavens.”

We didn’t know much at all about the Milky Way until Galileo pointed his telescope at it four centuries ago and wrote down that he saw individual stars.

“Up until the beginning of the 20th century that was basically it,” Lurie said. “The entire universe, as far as we knew, was contained in the Milky Way.”

New learning

Fast forward to Edwin Hubble, who used a much larger telescope, the 100-inch at Mt. Wilson, to look at cepheid variables. Hubble calculated that what was then known as the “Andromeda nebula” was about 2.5 million light years distant—way too far away to be part of our galaxy. It was another galaxy.

If this ball were the Sun, the next nearest star would be in
New York. Photo: Greg Scheiderer.

Galaxies seem awfully far-flung to be cannibalizing each other, but Lurie explained that they’re actually relatively close together. He noted that if the Sun were a yellow ball a bit smaller than a pint beer glass (an apt analogy given the locale of the talk) our next nearest stellar neighbor would be in New York. However, if the disk of the Milky Way galaxy were represented by a frisbee, the next nearest major galaxy would be inside Bad Jimmy’s, a mere 20 feet away. In addition, between us and Andromeda are a number of dwarf galaxies. Astronomers have found streams of stars that are evidence that the Milky way has collided with one of them, the Sagitarius dwarf galaxy.

“That’s why I claim that our galaxy is actually a cannibal,” Lurie said. “It’s in the process of eating this galaxy. Gravitational tidal forces of the Milky Way are tearing the stars off of this dwarf galaxy and they’re being strewn out into space.”

Bigger fish

Lurie says that when it comes to cannibal galaxies there’s always someone bigger out there.
“The Andromeda galaxy is coming to get us,” he said. “It’s a little bit bigger than us, and we’re on a collision course.”

Not to worry. It won’t happen for another four billion years or so, and since individual stars are so spread out, the likelihood that two would collide is pretty small. Some stars could get flung out of the galaxy, but mostly the Milky Way and Andromeda will eventually coalesce into one big galaxy.

Mining asteroids

Matt Beasley of Planetary Resources
explained the best types of asteroids
for mining useful materials.
Photo: Greg Scheiderer.

Closer to home folks are thinking of mining nearby asteroids for the valuable materials they contain. Dr. Matthew Beasley, a senior engineer at Redmond-based Planetary Resources, gave a talk titled, “Resources on Asteroids: What’s There, How Much, and Why?”

Beasley noted that there are 872 known asteroids of about one-kilometer orbiting in near-Earth space, and perhaps as many as 20,000 smaller ones down to about 100 meters. That’s a lot of potential targets for asteroid mining.

Why go to the trouble?

“Asteroids are extremely rich in useful materials,” Beasley said.
There are three main types of asteroids. Beasley explained that the first ones Planetary Resources will target are C-type carbonaceous asteroids. These make up about 75 percent of all asteroids, but only about six percent of the known near-Earth asteroids. They’re hard to spot because they’re so dark in color, like a lump of black clay. C-type asteroids are around 20 percent water by mass, and that’s what makes them appealing. Water is handy for space explorers to drink, and it can be broken down into hydrogen and oxygen for spacecraft fuel.

“One 75-meter C-type asteroid full of water could have fueled all of the shuttle missions,” Beasley noted. It will cost a lot less to pick up water and fuel in space than it does to launch them into space from Earth.

The second target type of asteroid is the M-type, which is heavily metallic. M-type asteroids contain virtually no water, but are rich in metals such as nickel, iron, and platinum, and maybe some silicates.

“One 500-meter metallic contains more platinum than has ever been mined by humanity,” Beasley said, adding that all of the platinum on Earth probably got here through collisions with asteroids. Platinum-group metals are highly sought after for electronics and other manufacturing, and all of the metals could be useful for building things in space. As with the water, it’s a lot less expensive to find it out there than it is to take it with you.

A third common asteroid is the stony S-type. These contain no water, some metals, but basically are between 75 and 90 percent silicates.

“They’re a little light on volatiles and organics, lots of rock,” Beasley said, noting there’s little interest in this type of asteroid. “Basically, they’re fill dirt.”

Game of Thrones and black holes at latest Astronomy on Tap

The extreme seasons on the popular HBO series Game of Thrones and supermassive black holes were the subjects of talks at the most recent Astronomy on Tap event held at Bad Jimmy’s Brewing Company in Ballard.

AoT vs. GoT: Reasons for the (Extreme) Seasons

Russell Deitrick makes a point during his talk at Astronomy on
Tap II at Bad Jimmy’s Brewing Company. Photo: Greg Scheiderer.

Russell Deitrick is an graduate student in astronomy at the University of Washington, studying models of the dynamics of exoplanets in multi-planet systems. He is particularly interested in how interactions between planets with high eccentricity and high mutual-inclination might affect habitability of those planets. That, it would seem, makes him the perfect one to figure out what could cause the sort of long, severe, and unpredictable seasons the characters on Game of Thrones experience.

Deitrick started with a quick primer on what causes seasons. The main cause is the axial tilt, or obliquity, of the planet. Earth, for example, has an axial tilt of about 23 1/2 degrees, and when a pole is inclined toward the Sun its hemisphere enjoys summer.

There are several ways to mess with the seasons, Deitrick explained. Our Moon stabilizes precession—the wobble of the orbital axis like a top—so if a planet doesn’t have a large moon, precession would be greater and there would be more variance. You could alter the orbit itself, making it highly eccentric.

Other factors that can change climate include volcanism, solar variability, or having a planet in a binary star system.

Deitrick ran computer models in which all of these varied wildly. The simulations didn’t match the show.

“Eccentricity can’t really explain the duration of the seasons on Game of Thrones,” Deitrick said. “If you’re at high eccentricity, you may have a very long winter, but you’re going to have a correspondingly short summer, and the seasons are going to be the same length.”

He noted that changing the obliquity of the axis can explain everything except the long duration of the seasons. Volcanos can create long seasons, but Deitrick said that doesn’t fit in with the show.

“The problem with the volcanic winter is that it’s possibly too random,” he said. “The fact that the seasons are quasi-predictable suggests that it probably isn’t related to volcanos.”

He said solar variability takes to long to create climate change on the short time scale of a season, and a binary star system doesn’t appear to be part of the story in Game of Thrones.

“You’d think they’d mention somewhere in the series that there were two suns,” he said.

“None of these can explain that long night, that generation of darkness,” Deitrick added.

“The seasons on Game of Thrones probably can’t be explained by a single theory,” Deitrick concluded. “So they’re probably magic.”

Supermassive black holes: size matters

Michael Tremmel is working on figuring
out how supermassive black holes came to be.
Photo: Greg Scheiderer.

Michael Tremmel, another UW astronomy grad student, took on an equally mysterious if less fictional topic in his Astronomy on Tap talk: supermassive black holes.

Tremmel explained that an ordinary black hole—one of between one and 10 solar masses—is the result of simple stellar evolution.

“When a massive star runs out of fuel and explodes in a supernova, the core of the star continues collapsing and forms a black hole,” he said.

The problem is that supermassive black holes can be of billions of solar masses and could not have formed in the same way.

“It’s still an open question where these black holes came from,” Tremmel said, “but we think that they must have formed very, very early on in the universe when the first stars that exist were beginning to form. Before there were galaxies, before there were stars, there were supermassive black holes.”

We’ve never seen a black hole because they don’t emit light. Their gravity is such that even light can’t break free. But the evidence that they exist is plain. Tremmel explained that we have observed stars orbiting rapidly around the center of our own galaxy. By gauging the trajectories of these stars we reach one conclusion about what they are orbiting.

“This object must be really, massive, and really, really small,” he said. “The only thing this thing could be is a black hole that is a billion solar masses.”

We’ve seen the evidence of black holes in other galaxies by catching the glow of gas as it is consumed by supermassive black holes.

“This gas is flowing in, spiraling around, and becoming very, very hot,” Tremmel noted. “As that gas gets really hot it emits a lot of light.”

Tremmel said it’s an exciting time for his field of study, trying to figure out more about the formation of supermassive black holes.

“These relatively tiny objects within a galaxy are a true mystery still for astronomers,” he said.

White spots on Ceres may be salt

The first big surprise as the Dawn spacecraft was approaching the dwarf planet Ceres earlier this year were bright white spots on its surface. Now that Dawn has been orbiting Ceres for six weeks, a theory has emerged about what the spots are: salt.

Dr. Tom McCord, a planetary physicist who is co-investigator on
the Dawn mission, spoke about the exploration of Ceres Saturday
during an Astronomy Day event at the Pacific Science Center
in Seattle. Photo: Greg Scheiderer.

Dr. Tom McCord, a co-investigator on the Dawn mission and director of the Bear Fight Institute, a research organization based in Winthrop, Wash., spoke at an Astronomy Day event Saturday at the Pacific Science Center in Seattle. Here’s why he thinks the spots could be salt.

McCord explained that Ceres is differentiated: it has a rocky core, a water-ice mantle layer, and a dirty crust. He noted that they’ve learned a lot from the early photographs.

“There’s a lot of evidence of activity; many craters, an older surface, but not as old as the object, so something obliterated the craters from early on,” McCord said. “Distorted features, so the surface had to have been warped.”

“There are domes, things pushing out from the inside,” he continued, “and bright spots that suggest that material from inside has come to the surface in some sort of volcanism.”

In addition, McCord explained that ground-based telescopes have detected water vapor that comes and goes in the area of Ceres. Liquid water from the interior of Ceres may be being ejected to the surface, where it wouldn’t last long.

This image was taken by NASA’s Dawn spacecraft of dwarf
planet Ceres on Feb. 19 from a distance of nearly 29,000
miles (46,000 kilometers). It shows that the brightest spot
on Ceres has a dimmer companion, which apparently lies
in the same basin.
Photo: NASA/JPL-Caltech/UCLA/MPS/DLR/IDA.

“What that would do is leave a residual salt deposit, so these bright spots could be salt deposits that accumulated around vents—volcanos—where the water is coming through,” McCord speculated.

He stresses that the work on data from Ceres is still in its early phases, joking that, “We scientists don’t know entirely what we are seeing.”

McCord said the evidence of geological activity has been the most interesting finding so far at Ceres.

“It has been active and may well still be active today,” he said. “That’s exciting to a physicist because you really want to know whether these processes that you conjure up in your models really have happened and, we hope to learn, to what extent and over what time scale.”

Ceres is a great target for study because it may hold clues to how planets form. It is the only dwarf planet in the inner solar system and is the largest object in the asteroid belt. With a diameter of 590 miles, it’s about as big as Texas.

“This is a very large small planet,” McCord said. Ceres comprises about a third of the mass of all objects in the asteroid belt.

The Dawn spacecraft is unique, according to McCord.

“It is the only interplanetary spacecraft that uses ion propulsion, and that is the only reason we are able to orbit two different objects in the outer solar system and still have enough fuel to go on,” he said. Dawn launched in 2007 and studied the asteroid Vesta for 14 months in 2011 and 2012 before heading to Ceres.

“Dawn is really a pathfinder for this kind of multiple-object extended exploration,” McCord said.

Dawn will be collecting data at Ceres for another year to 18 months. McCord said the spacecraft has four momentum wheels and needs three of them to hold itself in stable position. However two of the wheels have failed, so mission scientists are using the craft’s thrusters as a substitute. The hydrazine fuel will eventually run out, and Dawn will tumble about in a stable orbit around Ceres for a long, long time.