Black Hole Caught Red-Handed in a Stellar HomicideMay 03, 2012
Supermassive black holes, weighing millions to billions times more than the sun, lurk in the centers of most galaxies. These hefty monsters lie quietly until an unsuspecting victim, such as a star, wanders close enough to get ripped apart by their powerful gravitational clutches.
Astronomers had spotted these stellar homicides before, but this is the first time they have identified the victim. Using several ground- and space-based telescopes, a team of astronomers led by Suvi Gezari of the Johns Hopkins University, Baltimore, Md., identified the victim as a star rich in helium gas. The star resides in a galaxy 2.7 billion light-years away. The team's results appear in today's online edition of the journal Nature.
"When the star is ripped apart by the gravitational forces of the black hole, some part of the star's remains falls into the black hole, while the rest is ejected at high speeds," Gezari said. "We are seeing the glow from the stellar gas falling into the black hole over time. We're also witnessing the spectral signature of the ejected gas, 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 that the slaughtered star had to have been the helium-rich core of a stripped star."
This observation yields insights about the harsh environment around black holes and the types of stars swirling around them. It is not the first time the unlucky star had a brush with the behemoth black hole.
The team believes the star's hydrogen-filled envelope surrounding the core was lifted off a long time ago by the same black hole. The star may have been near the end of its life. After consuming most of its hydrogen fuel, it had probably ballooned in size, becoming a red giant. 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. On one of its close approaches, the star was stripped of its puffed-up atmosphere by the black hole's powerful gravity. The stellar remains continued its journey around the center, until it ventured even closer to the black hole to face its ultimate demise.
Astronomers predict stripped stars circle the central black hole of our Milky Way galaxy. These close encounters are rare, occurring roughly every 100,000 years. To find this event, Gezari's team monitored hundreds of thousands of galaxies in ultraviolet light with the Galaxy Evolution Explorer, and in visible light with Pan-STARRS1. Pan-STARRS, short for Panoramic Survey Telescope and Rapid Response System, scans the entire night sky for all kinds of transient phenomena, including supernovae.
The team was looking for a bright flare in ultraviolet light from the nucleus of a galaxy with a previously dormant black hole. Both telescopes spotted one in June 2010. Astronomers continued to monitor the flare as it reached peak brightness a month later and slowly faded during the next 12 months. The brightening event was similar to the explosive energy unleashed by a supernova, but the rise to the peak was much slower, taking nearly one-and-a-half months.
"The longer the event lasted, the more excited we got, because we realized this is either a very unusual supernova or an entirely different type of event, such as a star being ripped apart by a black hole," said team member Armin Rest of the Space Telescope Science Institute in Baltimore.
By measuring the increase in brightness, the astronomers calculated the black hole's mass to be several million suns, which is comparable to the size of our Milky Way's black hole.
Spectroscopic observations with the Multiple Meter Telescope Observatory on Mount Hopkins in Arizona showed the black hole was swallowing lots of helium. Spectroscopy divides light into its rainbow colors, which yields an object's characteristics, such as its temperature and gaseous makeup.
To completely rule out the possibility of an active nucleus flaring up in the galaxy, the team used NASA's Chandra X-ray Observatory to study the hot gas. Chandra showed that the characteristics of the gas didn't match those from an active galactic nucleus.
For images, video and more information about this study, visit: http://hubblesite.org/news/2012/18 .
For graphics and information about the Galaxy Evolution Explorer, visit: http://www.nasa.gov/galex and http://www.galex.caltech.edu
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. (Credit: NASA; S. Gezari, The Johns Hopkins University; and J. Guillochon, University of California, Santa Cruz)
Jet Propulsion Laboratory
Related Black Hole Current Events and Black Hole News Articles
'Perfect Storm' Quenching Star Formation around a Supermassive Black Hole
High-energy jets powered by supermassive black holes can blast away a galaxy's star-forming fuel, resulting in so-called "red and dead" galaxies: those brimming with ancient red stars yet containing little or no hydrogen gas to create new ones.
Strange Galaxy Perplexes Astronomers
With the help of citizen scientists, a team of astronomers has found an important new example of a very rare type of galaxy that may yield valuable insight on how galaxies developed in the early Universe. The new discovery technique promises to give astronomers many more examples of this important and mysterious type of galaxy.
A jettisoned black hole?
In his general theory of relativity, Albert Einstein predicted that there are such things as gravitational waves. In fact, the very existence of these waves is the linchpin of the entire theory.
NASA's Swift Mission Probes an Exotic Object: 'Kicked' Black Hole or Mega Star?
An international team of researchers analyzing decades of observations from many facilities, including NASA's Swift satellite, has discovered an unusual source of light in a galaxy some 90 million light-years away.
Unravelling the mystery of gamma-ray bursts
A team of scientists hope to trace the origins of gamma-ray bursts with the aid of giant space 'microphones'.
Research reveals the real cause of death for some starburst galaxies
Like hedonistic rock stars that live by the "better to burn out than to fade away" credo, certain galaxies flame out in a blaze of glory. Astronomers have struggled to grasp why these young "starburst" galaxies - ones that are very rapidly forming new stars from cold molecular hydrogen gas up to 100 times faster than our own Milky Way - would shut down their prodigious star formation to join a category scientists call "red and dead."
Mission to discover hundreds of black holes could unlock secrets of the universe
A team of Cardiff University researchers have made a breakthrough in helping scientists discover hundreds of black holes throughout the universe.
UCLA astronomers solve puzzle about bizarre object at the center of our galaxy
For years, astronomers have been puzzled by a bizarre object in the center of the Milky Way that was believed to be a hydrogen gas cloud headed toward our galaxy's enormous black hole.
New solar power material converts 90 percent of captured light into heat
A multidisciplinary engineering team at the University of California, San Diego developed a new nanoparticle-based material for concentrating solar power plants designed to absorb and convert to heat more than 90 percent of the sunlight it captures.
Lucky Star Escapes Black Hole With Minor Damage
Astronomers have gotten the closest look yet at what happens when a black hole takes a bite out of a star-and the star lives to tell the tale.
More Black Hole Current Events and Black Hole News Articles