Thursday, May 25, 2017

The big star that couldn’t become a supernova

One star's "massive fail" could solve a mystery

OSU - For the first time in history, astronomers have been able to watch as a dying star was reborn as a black hole.

It went out with a whimper instead of a bang.

The star, which was 25 times as massive as our sun, should have exploded in a very bright supernova. Instead, it fizzled out—and then left behind a black hole.

“Massive fails” like this one in a nearby galaxy could explain why astronomers rarely see supernovae from the most massive stars, said Christopher Kochanek, professor of astronomy at The Ohio State University and the Ohio Eminent Scholar in Observational Cosmology.

As many as 30 percent of such stars, it seems, may quietly collapse into black holes—no supernova required.

“The typical view is that a star can form a black hole only after it goes supernova,” Kochanek explained. “If a star can fall short of a supernova and still make a black hole, that would help to explain why we don’t see supernovae from the most massive stars.”

He leads a team of astronomers who have been using the Large Binocular Telescope (LBT) to look for failed supernovae in other galaxies. They published their latest results in the Monthly Notices of the Royal Astronomical Society.

Among the galaxies they’ve been watching is NGC 6946, a spiral galaxy 22 million light-years away that is nicknamed the “Fireworks Galaxy” because supernovae frequently happen there. Starting in 2009, one particular star, named N6946-BH1, began to brighten weakly. By 2015, it appeared to have winked out of existence.

It’s too early in the project to know for sure how often stars experience massive fails, but Scott Adams, a former Ohio State student who recently earned his Ph.D. doing this work, was able to make a preliminary estimate.

“N6946-BH1 is the only likely failed supernova that we found in the first seven years of our survey. During this period, six normal supernovae have occurred within the galaxies we’ve been monitoring, suggesting that 10 to 30 percent of massive stars die as failed supernovae,” he said.

He leads a team of astronomers who have been using the Large Binocular Telescope (LBT) to look for failed supernovae in other galaxies. They published their latest results in the Monthly Notices of the Royal Astronomical Society.

Among the galaxies they’ve been watching is NGC 6946, a spiral galaxy 22 million light-years away that is nicknamed the “Fireworks Galaxy” because supernovae frequently happen there. Starting in 2009, one particular star, named N6946-BH1, began to brighten weakly. By 2015, it appeared to have winked out of existence.

The astronomers aimed the Hubble Space Telescope at the star’s location to see if it was still there but merely dimmed. They also used the Spitzer Space Telescope to search for any infrared radiation emanating from the spot. That would have been a sign that the star was still present, but perhaps just hidden behind a dust cloud.

All the tests came up negative. The star was no longer there. By a careful process of elimination, the researchers eventually concluded that the star must have become a black hole.

It’s too early in the project to know for sure how often stars experience massive fails, but Scott Adams, a former Ohio State student who recently earned his Ph.D. doing this work, was able to make a preliminary estimate.

“N6946-BH1 is the only likely failed supernova that we found in the first seven years of our survey. During this period, six normal supernovae have occurred within the galaxies we’ve been monitoring, suggesting that 10 to 30 percent of massive stars die as failed supernovae,” he said.

"This is just the fraction that would explain the very problem that motivated us to start the survey.”

This illustration shows the final stages in the life of a supermassive star that fails to explode as a supernova but instead implodes under gravity to form a black hole. From left to right: the massive star has evolved to a red supergiant, the envelope of the star is ejected and expands, producing a cold, red transient source surrounding the newly formed black hole. Some residual material may fall onto the black hole, as illustrated by the stream and the disk, potentially powering some optical and infrared emissions years after the collapse.
Credits: NASA, ESA, and P. Jeffries (STScI)
To study co-author Krzystof Stanek, the really interesting part of the discovery is the implications it holds for the origins of very massive black holes—the kind that the LIGO experiment detected via gravitational waves. (LIGO is the Laser Interferometer Gravitational-Wave Observatory.)

It doesn’t necessarily make sense, said Stanek, professor of astronomy at Ohio State, that a massive star could undergo a supernova—a process which entails blowing off much of its outer layers—and still have enough mass left over to form a massive black hole on the scale of those that LIGO detected.

“I suspect it’s much easier to make a very massive black hole if there is no supernova,” he concluded.

Adams is now an astrophysicist at Caltech. Other co-authors were Ohio State doctoral student Jill Gerke and University of Oklahoma astronomer Xinyu Dai. Their research was supported by the National Science Foundation.

More information: S. M. Adams et al. The search for failed supernovae with the Large Binocular Telescope: confirmation of a disappearing star, Monthly Notices of the Royal Astronomical Society (2017). DOI: 10.1093/mnras/stx816 , On Arxiv:

The Ohio State University release is here.  The STScI news release (with additional pictures) is here.

- Christopher Kochanek, 614-292-5954;
- Krzysztof Stanek, 614-292-3433;
- Scott Adams, 626-395-8676;

Written by Pam Frost Gorder, 614-292-9475;

Sunday, May 14, 2017

The LBTO 2017 Users' Meeting preliminary program is out!


The preliminary program of the LBTO 2017 Users' Meeting is available here.

The list of the contributions (with their abstracts) sent so far can be found here.

More information on the Users' Meeting is available on its website.

Don't forget to register if you want to attend the meeting (and even more if you are presenting a talk or a poster!)

Wednesday, May 10, 2017


Taking advantage of a rare orbital alignment between two of Jupiter’s moons, Io and Europa, researchers have obtained an exceptionally detailed map of the largest lava lake on Io, the most volcanically active body in the solar system.

On March 8, 2015, Europa passed in front of Io, gradually blocking out light from the volcanic moon. Because Europa’s surface is coated in water ice, it reflects very little sunlight at infrared wavelengths, allowing researchers to accurately isolate the heat emanating from volcanoes on Io’s surface.

The infrared data showed that the surface temperature of Io’s massive molten lake steadily increased from one end to the other, suggesting that the lava had overturned in two waves that each swept from west to east at about a kilometer (3,300 feet) per day.

Overturning lava is a popular explanation for the periodic brightening and dimming of the hot spot, called Loki Patera after the Norse god. (A patera is a bowl-shaped volcanic crater.) The most active volcanic site on Io, which itself is the most volcanically active body in the solar system, Loki Patera is about 200 kilometers (127 miles) across. The hot region of the patera has a surface area of 21,500 square kilometers, larger than Lake Ontario.

Earthbound astronomers first noticed Io’s changing brightness in the 1970s, but only when the Voyager 1 and 2 spacecraft flew by in 1979 did it become clear that this was because of volcanic eruptions on the surface. Despite highly detailed images from NASA’s Galileo mission in the late 1990s and early 2000s, astronomers continue to debate whether the brightenings at Loki Patera -- which occur every 400 to 600 days -- are due to overturning lava in a massive lava lake, or periodic eruptions that spread lava flows over a large area.

“If Loki Patera is a sea of lava, it encompasses an area more than a million times that of a typical lava lake on Earth,” said Katherine de Kleer, a UC Berkeley graduate student and the study’s lead author. “In this scenario, portions of cool crust sink, exposing the incandescent magma underneath and causing a brightening in the infrared.”

“This is the first useful map of the entire patera,” said co-author Ashley Davies, of the Jet Propulsion Laboratory in Pasadena, who has studied Io’s volcanoes for many years. “It shows not one but two resurfacing waves sweeping around the patera. This is much more complex than what was previously thought.”

“This is a step forward in trying to understand volcanism on Io, which we have been observing for more than 15 years, and in particular the volcanic activity at Loki Patera,” said Imke de Pater, a UC Berkeley professor of astronomy.

De Kleer is lead author of a paper reporting the new findings that will be published May 11 in the journal Nature.

Binocular Telescope Turns Two Eyes on Io

The images were obtained by the twin 8.4-meter (27.6-foot) mirrors of the Large Binocular Telescope Observatory in the mountains of southeast Arizona, linked together as an interferometer using advanced adaptive optics to remove atmospheric blurring. The facility is operated by an international consortium headquartered at the University of Arizona in Tucson.

“Two years earlier, the LBTO had provided the first ground-based images of two separate hot spots within Loki Patera, thanks to the unique resolution offered by the interferometric use of LBT, which is equivalent to what a 23-meter (75-foot) telescope would provide,” noted co-author and LBTO director Christian Veillet. “This time, however, the exquisite resolution was achieved thanks to the observation of Loki Patera at the time of an occultation by Europa.”

Series of LBTI images showing Europa crossing the disk of Io (see here for more details)
Loki Patera is the bright hot spot in the upper part of the disk. Europa appears dark because water ice on its surface absorbs incident sunlight, while the sulfur dioxide ice on Io’s surface is less absorbing at this wavelength. Credit: LBTO

Europa took about 10 seconds to completely cover Loki Patera. “There was so much infrared light available that we could slice the observations into one-eighth-second intervals during which the edge of Europa advanced only a few kilometers across Io’s surface,” said co-author Michael Skrutskie, of the University of Virginia, who led the development of the infrared camera used for this study. “Loki was covered from one direction but revealed from another, just the arrangement needed to make a real map of the distribution of warm surface within the patera.”

These observations gave the astronomers a two-dimensional thermal map of Loki Patera with a resolution better than 10 kilometers (6.25 miles), 10 times better than normally possible with the LBT Interferometer at this wavelength (4.5 microns). The temperature map revealed a smooth temperature variation across the surface of the lake, from about 270 Kelvin at the western end, where the overturning appeared to have started, to 330 Kelvin at the southeastern end, where the overturned lava was freshest and hottest.

Using information on the temperature and cooling rate of magma derived from studies of volcanoes on Earth, de Kleer was able to calculate how recently new magma had been exposed at the surface. The results -- between 180 and 230 days before the observations at the western end and 75 days before at the eastern -- agree with earlier data on the speed and timing of the overturn.

Maps of the temperature and lava crust age within Loki Patera, derived from the LBTO observations. The higher temperatures in the southeast (location 3) indicate that new magma  was exposed most recently in this locatiaon. Credit: LBTO

Interestingly, the overturning started at different times on two sides of a cool island in the center of the lake that has been there ever since Voyager photographed it in 1979.

“The velocity of overturn is also different on the two sides of the island, which may have something to do with the composition of the magma or the amount of dissolved gas in bubbles in the magma,” de Kleer said. “There must be differences in the magma supply to the two halves of the patera, and whatever is triggering the start of overturn manages to trigger both halves at nearly the same time but not exactly. These results give us a glimpse into the complex plumbing system under Loki Patera.”

Lava lakes like Loki Patera overturn because the cooling surface crust slowly thickens until it becomes denser than the underlying magma and sinks, pulling nearby crust with it in a wave that propagates across the surface. According to de Pater, as the crust breaks apart, magma may spurt up as fire fountains, akin to what has been seen in lava lakes on Earth, but on a smaller scale.

De Kleer and de Pater are eager to observe other Io occultations to verify their findings, but they’ll have to wait until the next alignment in 2021. For now, de Kleer is happy that the interferometer linking the two telescopes, the adaptive optics on each and the unique occultation came together as planned that night two years ago.

“We weren’t sure that such a complex observation was even going to work,” she said, “but we were all surprised and pleased that it did.”

PIO Contacts:
UC Berkeley
Robert Sanders
+1 510-643-6998

University of Virginia
Fariss Samarrai
+1 434-924-3778

University of Liège
+32 4 366 52 17

Science Contacts:
Katherine de Kleer

Imke de Pater

Michael Skrutskie
+1 434-924-7494

Christian Veillet

Denis Defrère
+32 4 366 97 13

“Multi-Phase Volcanic Resurfacing at Loki Patera on Io,” K. De Kleer et al., 2017 May 11, Nature []. In addition to de Kleer, Skrutskie, Davies, Veillet and de Pater, co-authors of the paper are J. Leisenring, P. Hinz, E. Spalding and A. Vaz of the University of Arizona’s Steward Observatory, and Al Conrad of the Large Binocular Telescope Observatory, A. Resnick of Amherst College, V. Bailey of Stanford University, D. Defrère of the University of Liège, A. Skemer of UC Santa Cruz and C.E. Woodward of the University of Minnesota. The research was supported by the National Science Foundation.

Video 1 (reconstruction of the maps from the light curve):
Lower panels show the intensity of Loki Patera as a function of time as it is covered (ingress) and uncovered (egress) by Europa. The red curve is the model light curve corresponding to the intensity map shown above, the best-fit map to the observations. The animation shows Europa sweeping across the patera and obscuring different portions of its floor. Credit: Katherine de Kleer/UC Berkeley

Video 2 (simulation of the two-phase resurfacing):
The animation shows a schematic simulation of two resurfacing waves sweeping around the patera at different rates and converging in the southeast corner. Credit: Katherine de Kleer/UC Berkeley

Imke de Pater’s website:

Katherine de Kleer’s website:

The Large Binocular Telescope Observatory website:

Wednesday, March 29, 2017

A Trojan in retreat

For at least a million years, an asteroid orbiting the “wrong” way around the sun has been playing a cosmic game of chicken with giant Jupiter and about 6,000 other asteroids sharing the giant planet’s space, says a report published in the latest issue of Nature.

The asteroid is the only one in the solar system known to have an opposite, or retrograde, orbit around the sun while at the same time sharing a planet's orbital space, says researcher and co-author Paul Wiegert of University of Western Ontario’s Department of Physics and Astronomy.


Jupiter shares its orbit with more than 6,000 Trojan asteroids (white), which travel in the same direction as the planet. But one of the planet’s companions is an outlier, traveling in the opposite direction. Planets and asteroids  have been enlarged to make them visible. 
All but fewer than 100 of the million or so known asteroids in our solar system travel around the sun in the same direction as Earth and the other planets (prograde motion). But asteroid 2015 BZ509 (“BZ” for short) circles the other way around – moving against the flow of all other asteroids in the giant planet’s orbital entourage (retrograde motion).

Put another way, it’s as if Jupiter were a monster truck on a track circling the sun, and the asteroids in Jupiter’s orbit are sub-compact cars all whizzing along in the same direction. BZ is the rogue — driving around the track in the wrong direction — and it does so every single lap, and has done so for thousands of laps for a million years or more.

So how does it avoid colliding with Jupiter? Jupiter’s gravity actually deflects the asteroid’s path at each pass so as to allow both to continue safely on their way, Wiegert says. Co-author Martin Connors of Athabasca University, adds: “Passes relatively near Jupiter take place twice on each body's orbit around the sun, but one is inside Jupiter's orbit, the other outside, so the disturbing effects of Jupiter, remarkably, cancel out.“

Little is known about the asteroid, which was discovered in January, 2015. It has a diameter of about three kilometers and may have originated from the same place as Halley's comet, which also has a retrograde orbit. The team hasn’t been able to determine yet if BZ is an icy comet or a rocky asteroid.

Images of 2015 BZ509 obtained at the Large Binocular Telescope Observatory (LBTO) that established its retrograde co-orbital nature. The LBTO has two 8.4 meter-wide main mirrors side-by-side, hence the two images taken in different color filters. The bright stars and the asteroid (circled in yellow) appear black and the sky white in this negative image. What are those weird white dots, spots and stripes? They are imaging artifacts in these raw images.
But their analysis – based on complex calculations and on observations through the Large Binocular Camera on the Large Binocular Telescope (LBT) on Mt. Graham, Arizona, during a span of 300 days — show BZ is somehow able to maintain a stable orbit even as an outlier. For co-author Christian Veillet of the LBT Observatory, this is a new step in a 15-year-long collaboration among the three co-authors, which until now, has been devoted to prograde asteroids sharing Earth’s orbit.

The calculations conducted by the team show the orbit has been stable for at least a million years and will be stable for at least a million more. Learning more about the asteroid provides another intriguing glimpse into previously unknown and unmapped features of our solar system, says Wiegert, adding that “the detective work has just begun.”

More information and video clips are available here. The Letter in Nature can be found here.

Monday, January 9, 2017

2nd LBTO Users' Meeting - June 20,23 - Florence, Italy. Save the date!

The LBTO 2017 Users' Meeting will take place at the Convitto della Calza, Florence, Italy, from Tuesday evening, June 20 to Friday, June 23.

With the LBT facility instruments commissioned in pairs, LBTI routinely used by all partners in incoherent or coherent mode, LINC-NIRVANA en route for Lean-MCAO observing, and the ultra-high resolution of the PEPSI spectrograph available, the 2nd Users’ Meeting will focus on enabling LBT to realize its full potential as both a pair of 8.4m telescopes and, thanks to its interferometric capabilities, a forerunner of the ELTs. 

For current or prospective LBT users, the meeting will be an opportunity to share their scientific results, projects, and aspiration for the future of the observatory, foster boundary-crossing multi-partner collaborations, discuss new observing modes and new services with the observatory staff, and prepare for the next generation of instruments on the horizon for 2018-2019, all of which exploit the unique performance of the LBT's upgraded AO system.    

Please mark the date! You will find a first set of practical information (meeting place, links to hotel reservation, talk/poster submission) by visiting the Users' Meeting website here. For further questions on the meeting, contact either the Scientific Organizing Committee (soc-um @ or the Local Organizing Committee (loc-um @

A high-resolution picture of the  poster is available here.

LUCI1-AO Shared-Risk Science Release

Diffraction limited imaging with LUCI1 is offered in a shared-risk mode. Presently, the instrument is available for reference stars in the magnitude range 3.5 to 9.8 with degraded performance, and at design performance for fainter reference stars (down to ~16).  

It is expected that full AO performance with LUCI1, and diffraction limited imaging and spectroscopy with LUCI2, will become available in the course of 2017A. 

Observers new to AO are encouraged to consult the following references:
- Natural guide star adaptive optics systems at LBT: FLAO commissioning and science operations status, Esposito, et al., SPIE (2012)
- Field Guide to Adaptive Optics, Tyson & Frazier, SPIE Press (2012)
- Adaptive Optics and its Applications, C. Max, (click here)

A Notice to Users is available here.