Tag Archives: Astronomy on Tap Seattle

Calendar: SAS banquet and Astronomy on Tap Seattle this week

The annual Seattle Astronomical Society banquet and Astronomy on Tap Seattle are the highlight events for the coming week. The Museum of Flight kicks off Astronaut Remembrance Week, and regional planetarium shows cap the calendar.

SAS Banquet

Robert Reeves

Robert Reeves

The Seattle Astronomical Society banquet always draws an excellent guest speaker, and this year is no exception: renowned photographer Robert Reeves will keynote the annual banquet, and talk in particular about observing and imaging the Moon. The banquet gets under way at 4 p.m. Sunday, January 28 at the Swedish Club on Dexter Avenue North in Seattle. Reservations are $65 for the general public, $55 for SAS members. Don’t wait; there were only 18 spots left as of this writing. Reservations are available online.

Reeves will do a special master class on lunar photography for the SAS Astrophotography Special Interest Group. The class is open to the public and will be held at 5:30 p.m. Saturday, January 27 in the Red Barn Classroom at the Museum of Flight.

Astronomy on Tap Seattle

AOT Seattle January 2018The topic will be exploring alien moons when Astronomy on Tap Seattle holds its first event of the new year at 7 p.m. Wednesday, January 24 in the beer garden at Peddler Brewing Company in Ballard. Second-year UW graduate student in astronomy and astrobiology Tyler Gordon will speak about his research on the search for exoplanetary satellites using current and future telescopes. UW Ph.D. student in oceanography Max Showalter will discuss looking for life when the trail goes cold, an update on his work using movement as a sign of life in icy places.

Showalter did a talk at Town Hall Seattle almost two years ago. Check our recap of that talk and learn how SHAMU is helping hunt for ET.

Planetarium shows

The Washington State University Planetarium in Pullman has a new show this week titled, “Millions of Miles to Mars.” The show explores the whats, hows, and whens of Mars visits. Showtimes are 7 p.m. Friday, Jan 26, and 5 p.m. Sunday, Jan 28. Tickets at the door are $5 cash or check; they don’t accept credit cards. Kids under six get in free.

The Willard Smith Planetarium at the Pacific Science Center has a variety of shows for all ages every day. Check their website for the complete calendar.

Astronaut remembrance

America’s three great spacefaring tragedies all occurred at this time of year. To honor the sacrifices of the fallen astronauts, the Museum of Flight holds an annual astronaut remembrance week. The event runs from Friday, January 26 through Sunday, February 4 and features displays and exhibits about the fallen astronauts and their accomplishments. Solar System Ambassador Ron Hobbs will give a presentation about the tragic missions, and about the risks and successes of space travel, at 2 p.m. Saturday, January 27. It’s free with museum admission.

Future file

A total eclipse of the Moon will be visible in the early morning hours of Wednesday, January 31. The event begins just after 3 a.m. PDT, the partial eclipse starts around 3:45, and it will be total from just before 5 a.m. until a little after 6:00. All you really need to do is go outside and look up, but if you want to watch with others, the Seattle Astronomical Society plans a group viewing event at Solstice Park in West Seattle.

You can always scout out future events on our calendar.

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Merging neutron stars and cool galaxies at Astronomy on Tap Seattle

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.”

Neutron star merger animation by ESO/L. Calçada. Music: Johan B. Monell

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

Where stuff comes from

Periodic table showing origin of elements in the Solar System, by CMGLee on Wikimedia Commons based on data by Jennifer Johnson, Ohio State University.

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 showed the periodic table of elements at left (click to see it bigger), modified to show where all of the elements came from. She noted that hydrogen, helium, and a bit of lithium came from the Big Bang, the rest 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.

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Seeing the invisible and finding aliens using polarimetry

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

Lomax studies massive stars and has found use for polarimetry in her work. She gave a talk titled, “Seeing Invisible Circumstellar Structures.”

Jamie Lomax

Jamie Lomax

“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

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.

Astronomy on Tap Seattle is organized by graduate students in astronomy at the University of Washington. It’s next gathering is scheduled for October 30 at Peddler Brewing Company in Ballard.

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Learning about exoplanets with AoT Seattle

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.

Tovar

Lupita Tovar spoke about mapping exoplanets at Astronomy on Tap Seattle August 23, 2017. (Photo: Greg Scheiderer)

Lupita Tovar is a first-year Ph.D. student in astronomy and astrobiology at the University of Washington, where she works at the Virtual Planetary Laboratory. She gave a talk titled “Mapping New Worlds” at the most recent Astronomy on Tap Seattle event at Peddler Brewing Company in Ballard. Tovar is helping develop the parameters for LUVOIR, which stands for Large UltraViolet/Optical/InfraRed Surveyor. It is one of four projects being considered by NASA as part of the 2020 decadal survey, which will help pick the agency’s next big project.

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.

LUVOIR

Sketch of LUVOIR by NASA/Goddard

“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.

Windemuth

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.

Astronomy on Tap Seattle is organized by graduate students in astronomy at the University of Washington. The next gathering is scheduled for September 27 at Peddler Brewing Company in Ballard, and the topic will be polarimetry. We don’t know what that is, either, but are looking forward to finding out!

Astronomy on Tap plus Nordgren eclipse talk highlight week’s events

Another episode of Astronomy on Tap Seattle is on the calendar for this week, and astronomer, artist, and author Tyler Nordgren will visit the Museum of Flight to talk about his latest book about total solar eclipses.

The whole premise of Astronomy on Tap is that astronomy is even better with beer. This month we go even one step further, learning how beer isn’t possible without science as we go “From Stars to Beer.” The gathering will be at 8 p.m. Wednesday, July 26 at Peddler Brewing Company in Ballard.

AoT co-host Trevor Dorn-Wallenstein will give a talk titled, “An Unbeerlievable Tale: How atoms come together in stars to make the most glorious structure in the low-redshift universe: beer.” That may be the longest subtitle ever, too! Dr. Meredith Rawls will discuss her research about “Weighing Stars with Starquakes” with a fantastic technique called asteroseismology.

Astronomy on Tap Seattle is organized by graduate students in astronomy at the University of Washington. It’s free, but buy beer. Bring your own chair to create premium front-row seating in Peddler’s outdoor beer garden.

Nordgren on Eclipses

We’ve covered a number of talks by Tyler Nordgren over the last several years. Nordgren, astronomy professor at the University of Redlands, is also an author, artist, dark-sky advocate, and entertaining presenter. He’ll be at the Museum of Flight at 2 p.m. Saturday, July 29 to talk about his latest book, Sun Moon Earth: The History of Solar Eclipses (Basic Books, 2016).

The book is part travelogue covering some of Nordgren’s recent eclipse-chasing adventures, part history of eclipses and the myths and science surrounding them, and part primer for the total solar eclipse that will be visible from the United States next month. It’s a marvelous volume and we recommend it highly.

Nordgren spoke about the book at Town Hall Seattle back in January. You can read our re-cap of that talk and our review of the book. Nordgren will sign copies of Sun Moon Earth following his talk Saturday. Grab the book by clicking the book cover or link above; it helps Seattle Astronomy exist!

Star parties galore

The Seattle Astronomical Society will be involved in three star parties this weekend. The Covington Community Park star party will be held at 10 p.m. Friday, July 28 in said park. Volunteers from the Boeing and Tacoma societies also help out with this event.

SAS will hold its free monthly public star parties at 9 p.m. Saturday, July 29 at two locations: Green Lake in Seattle and Paramount Park in Shoreline. Bad weather cancels these star parties, so watch the SAS website or social media for updates. But hey, we’re on a good-weather roll!

Jazz Under the Stars

Jazz Under the StarsThe Tacoma Astronomical Society and Pacific Lutheran University physics department will lead stargazing at PLU’s Keck Observatory on Thursday, July 27 following the PLU Jazz Under the Stars concert. The artist for the free concert, which begins at 7 p.m. in the outdoor amphitheater of the Mary Baker Russell Music Center at PLU, is Anjali Natarajan, a Brazilian jazz vocalist out of Olympia. If the weather is bad the stargazing may be off, but the concert will just move indoors.

Jazz Under the Stars concerts will also be held on the next two Thursdays, August 3 and 10.


 

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

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 wierdly 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

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.

More information:

Morris’s talk on YouTube

Ted Talk by Tabetha Boyajian

 

A lighthearted look at the dark universe

Two astronomers recently came independently to the conclusion that the way to figure out the fate of the universe is to build bigger and better telescopes. Prof. Sarah Tuttle of the University of Washington and Dr. Ethan Siegel of the Starts With a Bang blog and podcast both made informative and entertaining presentations about the dark universe at the most recent gathering of Astronomy on Tap Seattle at Peddler Brewing Company in Ballard.

Sarah Tuttle

UW astronomy Prof. Sarah Tuttle spoke at Astronomy on Tap Seattle May 24, 2017 at Peddler Brewing in Ballard. (Photo: Greg Scheiderer)

In her talk titled, “Dark Matter, Dark Energy, and Otters,” Tuttle joked that astronomers are “the universal accountants,” and that right now these bean counters are thinking that 68 percent of the universal energy budget consists of dark energy.

“If I were you, I would be concerned, because I both just told you that most of the universal energy budget is dark energy, and we don’t know what it is,” Tuttle said. “Dark matter we can measure and observe, but we don’t know what that is, either.”

There are a lot of theorized particles that could be in the dark-matter mix, but Tuttle said we don’t really understand them yet.

“We are in the process of measuring them and trying to figure out what it could actually be that is dark matter, how it is interacting with everything around it, because it is the dominant form of matter in our universe,” she said. We’re even more in the dark about dark energy.

“We are able to pin down that dark energy exists, that the universe is expanding and accelerating, and we’re not yet quite sure how to explain that,” Tuttle said.

How do we know?

Three experiments have helped reveal dark energy. Observations of the cosmic microwave background and type 1a supernovae have shown us that the universe is expanding. Tuttle is involved with a project called HETDEX—the Hobby Eberly Telescope Dark Energy Experiment—using a 10-meter telescope in West Texas. HETDEX is taking spectra of faint, young galaxies that are Lyman-alpha emitters to try to detect baryon acoustic oscillations. Huh?

“We’re using the clustering of a particular kind of galaxy to measure the distortion of spacetime,” Tuttle explained. She said it’s like throwing a grid of lights over a three-dimensional object—the lights will reveal the shape of the object.

“We use these galaxies to show us the shape of spacetime underneath to expose how dark energy changes with time,” Tuttle said. Other efforts like EBOSS and the South Pole Telescope are working on the same problem.

“We use a lot of different techniques to try to figure out what we’re doing to expose what dark energy is,” Tuttle said. “It turns out it’s going to take more beer and more time before we can answer that question.”

Our fate is in dark energy’s hands

Ethan Siegel

Dr. Ethan Siegel of the Starts with a Bang blog and podcast spoke at Astronomy on Tap Seattle May 24. (Photo: Greg Scheiderer)

Siegel’s talk was titled “The Fate of the Universe: After 13.8 billion years, where is everything headed?” He noted that it astronomers once saw three possible scenarios for the future of our universe. It could keep on expanding forever, it could eventually collapse back onto itself, or expansion and gravity could balance out just right for a universe that remains about the way it is.

“That’s what we thought for years and years and decades and decades: the fate of the universe is going to be one of these three,” Siegel said. “The whole field of cosmology, which is my field, was the quest to measure what’s it going to be.”

“They’re all wrong,” he said. Dark energy is the wild card. Siegel pointed out that matter dilutes with the expansion of the universe, and radiation gets weaker; it redshifts. Dark energy? We’re not so sure.

“If there’s any type of energy that’s inherent to the fabric of space, then as space grows this energy is just growing,” Siegel explained. “As your universe grows, it’s like you’re just making more and more of this new type of energy if there’s any non-zero energy to space itself.”

A big assumption

Siegel gave a lengthy description of the fate of the universe, from the boiling oceans of Earth to the last black hole standing. It was all based on the assumption that dark energy is constant. But what if it gets stronger over time? Siegel said that would mean that galaxies and solar systems and the Earth would all get torn apart.

“In the fiery final moments, everything, even the atoms that made you up, even the nuclei that made you up, would be ripped apart as well,” he said. “That fate is known as the Big Rip, and it’s possible. I don’t think it’s right, but you can’t be sure unless you measure it.”

Dark energy could get weaker, too, and that could lead to the opposite outcome, a big crunch.

“That’s something we could also measure,” Siegel said. “We haven’t constrained it well enough to know that it won’t rip or that it won’t turn around and crunch again. The way we’re going to find out is through bigger and better telescopes and observatories.”

HETDEX is a big part of that, Siegel noted, and said that the ESA’s Euclid telescope will measure dark energy to better precision than ever before. NASA’s WFIRST (Wide Field Infrared Survey Telescope), scheduled to launch in mid-2020, and the Large Synoptic Survey Telescope, under construction in Chile with hopes of being fully operational by 2022, will also make key contributions to this work.

“If you think that this stuff is fun, I’m telling you it’s going to get even better in the 2020s,” Siegel concluded. Stay tuned.


If you couldn’t attend AOT Seattle, you can watch online! In May they live-streamed the event for the first time.

More reading:

  • Article about BOSS from a 2016 Astronomy on Tap
  • Article about the LSST from a 2016 Astronomy on Tap
  • Siegel’s talk about the expanding universe given to Rose City Astronomers in February
  • Siegel’s talk about the discovery of gravitational waves given to RCA in 2015
  • Siegel’s book, Beyond the Galaxy