Posted on by Nancy Atkinson

Black Holes are More Like Venus Fly Traps than Vacuum Cleaners

These images, taken with NASA's Galaxy Evolution Explorer (GALEX) and the Pan-STARRS1 telescope in Hawaii, show a galaxy that brightened suddenly, caused by a flare from its nucleus. Credit: NASA, S. Gezari (JHU), A. Rest (STScI), and R. Chornock (Harvard-Smithsonian CfA)

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I’m going to try and say this before the Bad Astronomer does: Holy Haleakala! A team of astronomers using the Pan-STARRS1 telescope on Mount Haleakala in Hawaii have found evidence of a black hole ripping a star to shreds. While this isn’t the first time this type of activity has been detected, these new observations are the best views so far of what happens to objects that are consumed by a black hole. Plus, astronomers, for the first time, know what kind of star was destroyed and watched as it happened. This all helps in providing more insight into how black holes behave: They aren’t enormous vacuum cleaners that suck up and destroy everything around them, or sharks that seek out and consume their victims. Instead, like Venus Fly Traps, they wait for objects to come to them.

“Black holes, like sharks, suffer from a popular misconception that they are perpetual killing machines,” said Ryan Chornock of the Harvard-Smithsonian Center for Astrophysics (CfA). “Actually, they’re quiet for most of their lives. Occasionally a star wanders too close, and that’s when a feeding frenzy begins.”

If a star passes too close to a black hole, tidal forces can rip it apart. The remaining gases then swirl in toward the black hole. But just a small fraction of the material near a black hole falls in, while most of it just circles for a while – sometimes forever. The material close the black hole gets superheated, causing it to glow. By searching for newly glowing supermassive black holes, astronomers can spot them in the midst of a feast.

So, kind of like with Junior, the giant Venus Fly Trap in the movie “Little Shop of Horrors,” the feast is evident from what doesn’t get eaten.

This computer simulation shows a star being shredded by the gravity of a massive black hole. Some of the stellar debris falls into the black hole and some of it is ejected into space at high speeds. The areas in white are regions of highest density, with progressively redder colors corresponding to lower-density regions. The blue dot pinpoints the black hole’s location. The elapsed time corresponds to the amount of time it takes for a Sun-like star to be ripped apart by a black hole a million times more massive than the Sun.

The team discovered this type of glow on May 31, 2010, with Pan-STARRS1 and also with NASA’s Galaxy Evolution Explorer (GALEX). The flare brightened to a peak on July 12th before fading away over the course of a year. The event took place in a galaxy 2.7 billion light-years away, and the black hole contains as much mass as 3 million Suns, making it about the same size as the Milky Way’s central black hole.

“We observed the demise of a star and its digestion by the black hole in real time,” said Harvard co-author Edo Berger.

“We’re also witnessing the spectral signature of the ejected gas, said Suvi Gezari of The Johns Hopkins University who lead the research, “which we find to be mostly helium. It is like we are gathering evidence from a crime scene. Because there is very little hydrogen and mostly helium in the gas we detect from the carnage, we know that the slaughtered star had to have been the helium-rich core of a stripped star.”

Follow-up observations with the MMT Observatory in Arizona showed that the black hole was consuming large amounts of helium. Therefore, the shredded star likely was the core of a red giant star. The lack of hydrogen showed this is likely not the first time the star had encountered the same black hole, and that it lost its outer atmosphere on a previous pass.

The star may have been near the end of its life, the astronomers say. After consuming most of its hydrogen fuel, it had probably ballooned in size, becoming a red giant. The astronomers think the bloated star was looping around the black hole in a highly elliptical orbit, similar to a comet’s elongated orbit around the Sun.

This computer-simulated image shows gas from a tidally shredded star falling into a black hole. Some of the gas also is being ejected at high speeds into space. Astronomers observed a flare in ultraviolet and optical light from the gas falling into the black hole and glowing helium from the stars's helium-rich gas expelled from the system. Credit: NASA, S. Gezari (The Johns Hopkins University), and J. Guillochon (University of California, Santa Cruz)

“This is the first time where we have so many pieces of evidence, and now we can put them all together to weigh the perpetrator (the black hole) and determine the identity of the unlucky star that fell victim to it,” Gezari said. “These observations also give us clues to what evidence to look for in the future to find this type of event.”

The team’s results were published today in the online edition of the journal Nature.

Nature Science Paper by S. Gezari et al. (PDF document)

Sources: Harvard Smithsonian CfA, NASA

Posted on by Nancy Atkinson

New Record: Telescope Finds 19 Near-Earth Asteroids in One Night

Richard Wainscoat (left) and Marco Micheli study one of the near-Earth asteroids found on January 29. The asteroid is the roundish dot near Wainscoat’s finger. Photo by Karen Teramura

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From a University of Hawaii Institute for Astronomy press release:

The Pan-STARRS PS1 telescope on Haleakala, Maui, discovered 19 near-Earth asteroids on the night of January 29, the most asteroids discovered by one telescope on a single night.

“This record number of discoveries shows that PS1 is the world’s most powerful telescope for this kind of study,” said Nick Kaiser, head of the Pan-STARRS project. “NASA and the U.S. Air Force Research Laboratory’s support of this project illustrates how seriously they are taking the threat from near-Earth asteroids.”

Pan-STARRS software engineer Larry Denneau spent that Saturday night in his University of Hawaii at Manoa office in Honolulu processing the PS1 data as it was transmitted from the telescope over the Internet. During the night and into the next afternoon, he and others came up with 30 possible new near-Earth asteroids.
Asteroids are discovered because they appear to move against the background of stars. To confirm asteroid discoveries, scientists must carefully re-observe them several times within 12-72 hours to define their orbits, otherwise they are likely to be “lost.”

Denneau and colleagues quickly sent their discoveries to the Minor Planet Center in Cambridge, Mass., which collects and disseminates data about asteroids and comets, so that other astronomers can re-observe the objects.

“Usually there are several mainland observatories that would help us confirm our discoveries, but widespread snowstorms there closed down many of them, so we had to scramble to confirm many of the discoveries ourselves,” noted Institute for Astronomy astronomer Richard Wainscoat.

Wainscoat, astronomer David Tholen, and graduate student Marco Micheli spent the next three nights searching for the asteroids using telescopes at Mauna Kea Observatories, Hawaii.

On Sunday night, they confirmed that two of the asteroids were near-Earth asteroids before snow on Mauna Kea forced the telescopes to close. On Monday night, they confirmed nine more before fog set in.
On Tuesday night, they searched for four, but found only one. After Tuesday, the remaining unconfirmed near-Earth asteroids had moved too far to be found again.

Telescopes in Arizona, Illinois, Italy, Japan, Kansas, New Mexico, and the United Kingdom, and the Faulkes Telescope on Haleakala also helped to confirm seven of the discoveries.

Two of the asteroids, it turns out, have orbits that come extremely close to Earth’s. There is no immediate danger, but a collision in the next century or so, while unlikely, cannot yet be ruled out. Astronomers will be paying close attention to these objects.

Posted on by Nancy Atkinson

Fully Functional Pan-STARRS is now Panning for Stars, Asteroids and Comets

Pan-STARRS PS1 Observatory. Image courtesy of Rob Ratkowski Photography and the Haleakala Amateur Astronomers.

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There’s a new eye on the skies on the lookout for ‘killer’ asteroids and comets. The first Pan-STARRS (Panoramic Survey Telescope & Rapid Response System) telescope, PS1, is fully operational, ready to map large portions of the sky nightly. It will be sleuthing not just for potential incoming space rocks, but also supernovae and other variable objects.

“Pan-STARRS is an all-purpose machine,” said Harvard astronomer Edo Berger. “Having a dedicated telescope repeatedly surveying large areas opens up a lot of new opportunities.”

“PS1 has been taking science-quality data for six months, but now we are doing it dusk-to-dawn every night,” says Dr. Nick Kaiser, the principal investigator of the Pan-STARRS project.

Pan-STARRS PS1 Observatory just before sunrise on Haleakala, Maui. Credit: Harvard-Smithsonian Center for Astrophyiscs

Pan-STARRS will map one-sixth of the sky every month and basically be on the lookout for any objects that move over time. Frequent follow-up observations will allow astronomers to track those objects and calculate their orbits, identifying any potential threats to Earth. PS1 also will spot many small, faint bodies in the outer solar system that hid from previous surveys.

“PS1 will discover an unprecedented variety of Centaurs [minor planets between Jupiter and Neptune], trans-Neptunian objects, and comets. The system has the capability to detect planet-size bodies on the outer fringes of our solar system,” said Smithsonian astronomer Matthew Holman.

Pan-STARRS features the world’s largest digital camera — a 1,400-megapixel (1.4 gigapixel) monster. With it, astronomers can photograph an area of the sky as large as 36 full moons in a single exposure. In comparison, a picture from the Hubble Space Telescope’s WFC3 camera spans an area only one-hundredth the size of the full moon (albeit at very high resolution).

This sensitive digital camera was rated as one of the “20 marvels of modern engineering” by Gizmo Watch in 2008. Inventor Dr. John Tonry (IfA) said, “We played as close to the bleeding edge of technology as you can without getting cut!”

Each image, if printed out as a 300-dpi photograph, would cover half a basketball court, and PS1 takes an image every 30 seconds. The amount of data PS1 produces every night would fill 1,000 DVDs.

Another view of Pan STARRS PS1 Observatory. Image courtesy of Rob Ratkowski Photography and the Haleakala Amateur Astronomers.

“As soon as Pan-STARRS turned on, we felt like we were drinking from a fire hose!” said Berger. He added that they are finding several hundred transient objects a month, which would have taken a couple of years with previous facilities.

Located atop the dormant volcano Haleakala (that’s Holy Haleakala to you, Bad Astronomer) Pan-STARRS exploits the unique combination of superb observing sites and technical and scientific expertise available in Hawaii.

Source: CfA