Category Archives: lectures

Learning about LIGO at Astronomy on Tap

The most recent gathering of Astronomy on Tap Seattle brought to town two scientists working in one of the most groundbreaking areas of astronomy: detection of gravitational waves.

Nature was kind to us

Jeff Kissel, a control systems engineer at the LIGO Hanford Observatory, talked about how exciting it was when they switched on advanced LIGO back in September 2015.

“Boom! Right out of the gate we saw this whopper of an event,” Kissel said, detecting gravitational waves from the merger of a pair of stellar-mass black holes. “Nature was very kind to us.”

What they spotted at Hanford and at LIGO in Livingston, Louisiana was a match.

“Inside our data, which is almost always noise, we saw this very characteristic wave form that was predicted by general relativity,” Kissel recalled. They found gravitational waves from a couple of other black-hole mergers in the following months.

“This is the beginning of gravitational wave astronomy,” Kissel said.

Gravitational waves oscillate through spacetime in a way
by this animation. Credit: ESA–C.Carreau

Kissel pointed out that LIGO only detects a small part of the gravitational wave spectrum. As with light, gravitational waves can come in a wide range of wavelengths with periods ranging from milliseconds to billions of years. Longer-length waves might come from the mergers of galactic nuclei, or even from quantum fluctuations from the early universe.

“There’s a whole zoo of things to find out there,” Kissel said. He anticipates more ground-based observatories as well as some space LIGOs that could have detector arms millions of kilometers long.

How LIGO works

LIGO sounds awfully complicated, but, broken down, the idea is pretty simple. Jenne Driggers
is a Caltech postdoctoral scholar stationed at the LIGO Hanford Observatory, where her gig is improving the sensitivity of the interferometers. Driggers explained that, essentially, they shoot a laser beam into a splitter that sends beams down two equal arms four kilometers long. The beams reflect from mirrors and return to be put back together.

A simplified look at how LIGO works. A laser beam is split and sent down two equal
arms four kilometers long, then reflected back by mirrors. When they return to be
recombined, they will usually cancel each other out and no light will get to the detector.
But if a gravitational wave distorts the system, the light will be spotted by the detector.
Credit: T. Pyle, Caltech/MIT/LIGO Lab

“When they recombine they can be exactly out of phase, and then there’s no laser light (at the detector),” Driggers said. “They cancel each other out totally. Or the lengths will change and these two electromagnetic waves can add up, and so we do get some light.”

When that happens it means that a gravitational wave has distorted the LIGO arms ever so slightly. They measure the light received at the detector to learn more about the wave.

In practice it’s a lot more complicated. It all happens in a total vacuum to avoid any distortion from air. The mirrors are suspended from a system of four pendulums, which helps to eliminate vibration. The mirrors are highly reflective pieces that each weigh around 100 pounds and cost half a million dollars. The laser is about the best there is.

“The laser wavelength itself is our ruler that we’re using to measure the distance between those two mirrors,” Driggers said, “and we need to be able to measure that distance to 10-19 meters.”

“This is one of the highest-power, frequency stable, power-stable lasers on the planet,” she added.

Driggers invited people to tour LIGO Hanford. Public tours are held twice each month, and groups of 15 or more can arrange for a private tour.

Up next: LSST

Astronomy on Tap Seattle is presented and organized by astronomy graduates students at the University of Washington. Their next event is planned for Friday, October 28 at Peddler Brewing Company in Ballard and will feature UW scientists Dr. John Parejko and Dr. David Reiss, who are working on the Large Synoptic Survey Telescope project. The events are free. Enjoy beer and astronomy!


Astronaut visit a hot ticket this week

An astronaut visit to Seattle is the highlight of this week’s area astronomy calendar, but if you don’t have a ticket already you may be out of luck.

Spaceman: An Evening With Astronaut Mike Massimino will be happening at 5:30 p.m. Friday, October 14 at the Museum of Flight, but as of this writing the event is sold out. The evening’s events include a reception, lecture, and signing of Massimino’s new book Spaceman: An Astronaut’s Unlikely Journey to Unlock the Secrets of the Universe (Crown Archetype, 2016). Massimino is a veteran of two space shuttle missions, including the final servicing mission to the Hubble Space Telescope. If you’d like to go to Friday’s event, you might watch the museum’s website in case additional tickets become available or a waiting list is established. You can pick up the book, at least, at the link above or by clicking the photo at left.

The Boeing Employees’ Astronomical Society will hold its monthly meeting Thursday, October 13, with social time starting at 6:30 p.m. and the evening program beginning at 7 p.m. The meeting will be held in the Boeing “Oxbow” Recreation Center, Building 9-150, Room 201. Non-Boeing attendees are welcome but will need an escort; visit the website for details.

haunted-night-skyIt’s Spook-tober at the Pierce College Science Dome, which will be presenting a kids’ show called “Haunted Night Sky” on Saturdays through Halloween. Participants will be able to find creatures in the night sky, build a Frankenstein satellite, and take a tour of the Sea of Serpents on the Moon, the Witch’s Head Nebula, and other spooky places in the universe. Best for kids ages 3-12. Shows are scheduled for 12:30 p.m. and 2 p.m. each Saturday. Cost is $3.

Futures file

You can scout out future astronomy events on our calendar. New additions to the calendar this week include:

Up in the sky

Eagle-eyed early birds can spot Mercury and Jupiter together in the east just before dawn on October 11. The Sky This Week from Astronomy magazine and This Week’s Sky at a Glance from Sky & Telescope have more observing highlights for the week.


Equinox sunset watch, Tyson visit highlight week’s calendar

A visit from astrophysicist Neil deGrasse Tyson, the final Jacobsen Observatory open house of the year, and a seasonal sunset watch are the highlights of this week’s calendar of astro-events in the Seattle area.

Tyson, director of the Haden Planetarium in New York, narrator of the recent Cosmos television series, author, and host of the StarTalk radio show and podcast, will speak at Seattle’s Paramount Theatre on two nights this week, Wednesday, September 21 and Thursday, September 22, both at 7:30 p.m. Some tickets are still available for both appearances.

Ring in autumn

AlicesAstroInfo-145Join Alice Enevoldsen of Alice’s Astro Info at Solstice Park in West Seattle at 6:30 p.m. Thursday, September 22 to enjoy the first sunset of autumn. The equinox sunset watch will be Enevoldsen’s thirtieth such event, part of her NASA Solar System Ambassador service. The event is free, low-key, and always informative.

TJO wraps its season

Theodor Jacobsen ObservatoryThe final open house of the year is set for 8 p.m. Wednesday, September 21 at the Theodor Jacobsen Observatory on the University of Washington campus in Seattle. The talk for the evening, reservations for which are already all spoken for, will be by student Anya Raj, who has been interning with NRAO-NM over the summer and who has built a dual-dipole radio telescope. Raj will talk about amateur radio astronomy and making your own radio telescope. Volunteers from the Seattle Astronomical Society will be on hand in the observatory dome to conduct tours and, if the sky is clear, offer looks through its vintage telescope.

The popular open house series will be on hiatus for the fall and winter and will resume in April.

Club events

Seattle Astronomical SocietyThe Seattle Astronomical Society will hold its monthly meeting at 7:30 p.m. Wednesday, September 21 in room A102 of the Physics/Astronomy Building on the University of Washington campus in Seattle. Guest speaker Ethan Kruse, a graduate student in astronomy at the UW, will talk about Proxima Centauri b, the exoplanet recently found orbiting our nearest stellar neighbor. Kruse will discuss how much we know about the planet right now, and what we might learn in the coming years.

By way of preview, check our articles about a talk by Kruse at an Astronomy on Tap Seattle event from earlier this year, and about a presentation by Prof. Rory Barnes at Pacific Science Center last month exploring the potential habitability of the planet.

Tacoma Astronomical SocietyThe Tacoma Astronomical Society plans one of its public nights for 9 p.m. Saturday, September 24 at the Fort Steilacoom campus of Pierce College. The indoor presentation will be about the reasons for the seasons as we shift into fall. Weather permitting, club members will have telescopes out for looking at the sky.

Futures file

You can scout out future astronomy events on our calendar. New additions to the calendar this week include:

  • World Space Week events October 4–7 at the UW Planetarium
  • The BP Astro Kids November 12 look at the craters of the Moon

Up in the sky

The ice giants Uranus and Neptune are well-placed for observing this week. The Sky This Week from Astronomy magazine and This Week’s Sky at a Glance from Sky & Telescope offer additional observing highlights for the week.


Proxima Centauri b and the question of habitability

The discovery of evidence of a planet in orbit around our nearest stellar neighbor, Proxima Centauri, has people all agog and with good reason. It’s something of a misnomer, however, to call the exoplanet Proxima Centauri b “Earth-like.” Rory Barnes, a professor in the Department of Astronomy and the Astrobiology Program at the University of Washington, points out that the planet’s mass is probably somewhere between 1.3 and five times that of Earth.


UW prof. Rory Barnes speaking at an Astronomy on Tap Seattle event earlier this year. Photo: Greg Scheiderer.

“There’s a lot of excitement about this planet because it is so close in mass to the Earth, but we don’t actually know if it’s even rocky like the Earth,” said Barnes during a recent talk at the Pacific Science Center. Barnes, who uses computer modeling to study the habitability of exoplanets, noted that even though Proxima Centauri is the next closest star, it’s still pretty far away at 4.24 light years. If the Sun were the size of a baseball resting on home plate at Safeco Field, Barnes said Proxima Centauri b would be a grain of sand in New York City. Still, he noted there’s understandable excitement about the discovery.

“The reason why I think that this is the biggest exoplanet discovery since the discovery of exoplanets is because it is still very close, at least relatively speaking,” Barnes said. “We really have a chance, with this planet, to potentially observe its atmosphere and its surface and maybe start to try and sniff out the presence of life on that planet. Or not. We don’t know yet. But being so close, it gives us a shot.”

Not really “like” Earth

While Proxima Centauri b is about the mass of Earth, plenty else is different. It’s twenty times closer to its home star than Earth is to the Sun, and goes around that star in just 11.2 days. We know little else about it. The star has just 12 percent of the mass and 14 percent the radius of the Sun, and its brightness is just one one-thousandth that of the Sun.

“This is a small, dim star,” Barnes said.

Is there life there?

Life requires energy, some bioessential elements, and liquid water. The energy and elements are abundant in the universe, so Barnes says the key to finding life elsewhere is liquid water.

“When we think about exoplanets, we’re really going to focus, at least for now, on surface water,” Barnes said. “Not only is it going to be easier to see, but it’s going to be more similar to the Earth and that gives us a better shot at maybe being able to interpret the observations that we’re going to get.”

The desire to find liquid surface water on a planet led us to the concept of the “habitable zone” around a star, an area where the temperature would be right for liquid water to exist. Barnes said Proxima Centauri b is smack in the middle of the habitable zone.

“This is a dream planet for those of us who study this field,” he said, but added a caveat: “Being in the habitable zone does not mean you’re habitable. It is just the first step we need to get to.”

“The habitable zone is jargon, and it’s really misleading,” Barnes added. “I apologize for my field for inflicting it on you!”

Barnes said there are several threats to habitability for planets orbiting M dwarf stars like Proxima Centauri. With the habitable zone so close to the star, there is potential that stellar flares could blow away the atmosphere of a planet within it. Planets that close are probably tidally locked, too, but this isn’t a deal-breaker; their atmospheres might distribute heat and energy effectively. Tidal heating could cause problematic volcanism.

Habitable zone chart

Barnes showed this chart demonstrating that while Proxima Centauri b is now within the habitable zone, the zone was once much further from the star.

The biggest threat to the habitability of Proxima Centauri b, according to Barnes, is that its star was once much bigger and brighter before it contracted into the dim, red phase it is in today. In the early years that would have meant that its habitable zone was out at a distance between .25 and .5 astronomical units, while Proxima Centauri b orbits at a mere .05 AU. Being so far inside the habitable zone after formation means that the planet could have lost all of its water and become a completely uninhabitable place like Venus. On the other hand, if Proxima Centauri b formed as something like Neptune, being so close to the star could have blasted away its hydrogen envelope.

“Maybe that planet could have actually transformed from an uninhabitable Neptune-like planet into a rocky planet like the Earth,” Barnes speculated. “This is what we at the University of Washington think is probably the best bet for how this planet could be habitable.”

Barnes is hopeful that the discovery of Proxima Centauri b will help boost support for the sorts of telescopes and observatories that can make the observations needed to learn more about this intriguing exoplanet and determine if it is habitable, and even inhabited.

While Barnes won’t give the odds of life there—there are way too many variables and so little we know right now—he sounds confident that we’ll find life somewhere. He noted that we’ve found life on Earth in the deep sea, extreme deserts, extreme cold, acidic environments, and under other harsh conditions.

“The realization that extreme life is everywhere is part of the astrobiological revolution that is occurring right now in science,” Barnes said. “This recognition that life finds a way gives us confidence as we go forward.”


Annual Moon viewing festival highlights week’s calendar

The last installment of the Pacific Science Center’s Science Café series and an annual Moon viewing festival are the high points of this week’s astronomy events calendar.

Viewing the Moon

Seattle Japanese GardenThe popular annual Moon Viewing Festival at the Seattle Japanese Garden will be held beginning at 6 p.m. Saturday, September 17 at the garden, which is within the Washington Park Arboretum in Seattle. The evening will include music, a haiku contest, and a traditional Japanese Tea Ceremony. Volunteers from the Seattle Astronomical Society will be on hand with telescopes to offer a great, close-up view of the Moon. Unfortunately, as of this writing the event is sold out.

Farewell to the science café

Pacific Science CenterThe Pacific Science Center is discontinuing its Science Café program after more than ten years at The Swiss Restaurant & Pub in Tacoma, Wilde Rover in Kirkland, and, up until a year or two ago, T.S. McHugh’s in Seattle. The center plans to have many of the same sorts of speakers and topics at its new, onsite Science in the City lectures.

One final astronomy-themed science café remains on the calendar and will be held at The Swiss at 6:30 p.m. Tuesday, September 13Josh Krissansen-Totton of the University of Washington Astrobiology Program and Department of Earth and Space Sciences will give a talk titled “The Search For Life Beyond Earth.” Krissansen-Totton will go beyond the headlines and explore how astronomers and astrobiologists are trying to detect life on exoplanets, and when they’re likely to be successful. Admission is free. Bring questions; there’s always plenty of time for Q-and-A.

OAS meets

Olympic Astronomical SocietyThe Olympic Astronomical Society will hold its monthly meeting at 7:30 p.m. Monday, September 12 in room Art 103 at Olympic College in Bremerton. They plan to make a comet, among other activities.

Futures file

You can scout out future astronomy events on our calendar. New additions this week include:

Up in the sky

September often offers great weather for stargazing as it’s still typically fairly warm in the evenings but the nights are getting longer. This Week’s Sky at a Glance from Sky & Telescope magazine and The Sky This Week from Astronomy have observing highlights for the week.


Wednesday astronomy at UW

Most of the week’s astronomy activity is focused on a couple of events Wednesday at the University of Washington.

Seattle Astronomical SocietyThe Seattle Astronomical Society will hold its monthly meeting at 7:30 p.m. Wednesday, June 15 in room A102 of the Physics/Astronomy building on the Seattle campus. Society member John McLaren will give a presentation about solar exploration, covering early human interactions with the Sun and their unexpected impacts on our growing technology. He’ll discuss how we learned about the Sun before the space age, what we’ve since discovered from space-based observing, and what the future holds for solar observations from space. The meeting is open to the public.

TJO goes retrograde

Theodor Jacobsen Observatory

Photo: Greg Scheiderer.

After the SAS gathering you’ll have just enough time to dash up campus to one of the twice-monthly open houses at the Theodor Jacobsen Observatory, which begins at 9 p.m. With both Mars and Saturn in the retrograde parts of their orbits, the observatory director, Dr. Ana Larson, will talk about what that means, will discuss the historical context, and help visitors plot the motion of Mars against the background stars using a star map.

With both planets well placed for viewing, hope for clear skies and at peek at them through the observatory’s vintage telescope, operated by volunteers from the Seattle Astronomical Society.


The Willard Smith Planetarium at Pacific Science Center has several astronomy shows every day. Check our calendar for the schedule.

Pacific Planetarium in Bremerton will offer public shows on Friday, June 17, with hourly presentations at 5 p.m., 6 p.m., and 7 p.m. The topic will be star hopping: how to explore the heavens using the constellations and stars as a guide. Admission to the shows is $5.

Up in the sky

Jupiter, Mars, and Saturn all remain well placed for evening viewing these days, but there’s plenty more to see. The Sky This Week from Astronomy magazine and This Week’s Sky at a Glance from Sky & Telescope have other observing highlights for the week.


Space oddities at Astronomy on Tap Seattle

Things got a little strange at the most recent gathering of Astronomy on Tap Seattle, and not just because we were all drinking beer at Hilliard’s Beer Taproom in Ballard and enjoying eats from the Cave Man Food Truck parked outside. The event, organized by astronomy graduate students at the University of Washington, took on space oddities like Hanny’s Voorwerp and Thorne-Żytkow Objects.

Seattle Astronomy gets all sentimental about Hanny’s Voorwerp because it has a cool name and it was a subject of our third post ever when we started this effort in January 2011. The Voorwerp was noticed by Hanny van Arkle, a Dutch schoolteacher who was categorizing galaxies in Sloan Digital Sky Survey images as part of the Galaxy Zoo project. The object (voorwerp is Dutch for thing or object) appeared as a blue blob near the galaxy IC 2497.

What’s a voorwerp?

John Ruan

Graduate Student John Ruan spoke about Hanny’s Voorwerp at Astronomy on Tap Seattle May 25. Photo: Greg Scheiderer.

During his talk titled, “Citizen Discovers Strange Black Hole Echoes: The Science Behind Hanny’s Voorwerp,” UW graduate student John Ruan said there were four ideas about what it was. All of them were wrong.

Imaging artifact. It could have been just a blip on the camera, Ruan said, but other observers were able to spot it.

Unknown solar system object. Ruan said solar system objects move rapidly, but the Voorwerp was found on photographic plates made more than 50 years ago, and it hadn’t budged.

Distant, high-redshift galaxy. The redshift was not high enough for the Voorwerp to be at great distance.

Milky Way nebula. Conversely, it wasn’t something in our own galaxy, either, this time because the redshift was not great enough.

It was in examining the spectra, though, that Ruan said a clue was found. The emission lines were strong.

“To get emission lines that are this strong, you need a really, really bright source that emits a lot of high-energy light,” Ruan said, the kind of light you get from gas falling onto a black hole. “This is evidence that this object was produced by a quasar.”

Hanny's Voorwerp

Hanny’s Voorwerp appears as a green blob in this photo by NASA, ESA, W. Keel (University of Alabama), and the Galaxy Zoo Team.

There was just one small problem with the idea. There’s no quasar in any of the photos. Ruan said the quasar was probably created when the galaxy merged with a smaller one.

“It disturbs the gas in this larger galaxy, and this gas, some of it, because it’s disturbed it will fall into the center of the galaxy and fall into the black hole,” Ruan explained. This ignited the quasar, but at some point it literally ran out of gas.

“That quasar became quiet again, and it looked like just a normal galaxy, however the gas cloud that the quasar was shining on still appears to be lit up,” he said. “And that is Hanny’s Voorwerp.”

Similar objects have been discovered and are generally referred to as quasar ionization echoes. Ruan said Hanny’s Voorwerp will gradually fade as the ionization of the gas wears off.

The weirdest stars in the universe

Emily Levesque is just finishing her first year on the astronomy faculty at the University of Washington, and her research bailiwick fit perfectly into space oddity night.

Emily Levesque

Emily Levesque makes a point about TZOs. Photo: Greg Scheiderer.

“I study weird stars, strange stars, the really oddball stars that we can’t easily explain,” Levesque said. Indeed, she started out looking at the odd couple of stars: red supergiants and neutron stars.

Red supergiants are enormous, massive, relatively cool stars. The largest one found so far is so big that it’s surface, if it were plunked into our solar system in place of the Sun, would reach almost out to the orbit of Saturn. Neutron stars are the small, dense remains of supernovae. They are no bigger than a city.

“There’s only one thing that I can do to red supergiants and neutron stars to make them weirder at this point,” Levesque said. “If we put a red supergiant and a neutron star into a binary, and we merge them, we get a very, very weird object.”


The weird object is called a Thorne-Żytkow Object (TŻO) because Kip Thorne of Caltech and Anna Żytkow of the University of Cambridge hypothesized just this sort of thing way back in 1977. Żytkow heard that Levesque was studying red supergiants, and sent an email asking if she’d like to give a shot at spotting a TŻO. It was quite a challenge.

“A neutron star is the size of the city of Seattle,” Levesque said. “A red supergiant is bigger than the orbit of Jupiter. If you embed a neutron star inside a red supergiant it’s virtually impossible to detect.”

As with Hanny’s Voorwerp, the spectra were the key. Inside a TŻO, convection pockets would circulate material and create bizarre chemical processes. As stuff nears the neutron star at the core it would be bombarded with protons, changing it into a different element. Then as it nears the surface of the star, it would decay into yet something else. The process repeats. If the spectrum reveals the presence of elements that you would not normally expect to see at the surface of a cold star, you may be onto something.

Two years ago Levesque and her team looked at 100 red supergiants, and 99 of them appeared normal. The spectrum of one of them, HV 2112, showed unusual concentrations of rubidium, lithium, and molybdenum.

“This was a signature that we’d actually found the first example of a Thorne-Żytkow Object in the universe,” Levesque said.

If true, it means a new way to make stars and a new way to make elements. Levesque said they’re still calling the star a candidate or possible TŻO because of the Sagan Standard that holds that extraordinary claims require extraordinary evidence.

“The evidence that we have is really compelling, but it’s three little blips in a spectrum,” Levesque said. “We desperately want to find more of these, we want to find other ways of detecting them. We’d ultimately love to have a whole set of Thorne-Żytkow Objects, and have a whole set of stars that we can look at that can hold the title of weirdest star in the universe.”