Black Hole Caught Red-Handed in a Stellar Homicide
PASADENA, Calif. – Astronomers have gathered the most direct evidence yet of a supermassive black hole shredding a star that wandered too close. NASA's Galaxy Evolution Explorer, a space-based observatory, and the Pan-STARRS1 telescope on the summit of Haleakala in Hawaii were among the first to help identify the stellar remains.
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.
These images, taken with NASA's Galaxy Evolution Explorer and the Pan-STARRS1 telescope in Hawaii, show a brightening inside a galaxy caused by a flare from its nucleus. Image credit: NASA/JPL-Caltech/JHU/STScI/Harvard-Smithsonian CfA
› Full image and caption
"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.
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 the flare in ultraviolet light
using NASA's Galaxy Evolution Explorer, and in optical light using the
Pan-STARRS1 telescope on Mount Haleakala, Hawaii. The light comes from
gas falling into the black hole, and glowing helium from the star's
helium-rich gas expelled from the system. Image credit:
NASA/JPL-Caltech/JHU/UCSC
› Larger view
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 .
Jet Propulsion Laboratory, Pasadena, Calif.
Whitney.clavin@jpl.nasa.gov
J.D. Harrington 202-358-0321
Headquarters, Washington
j.d.harrington@nasa.gov
2012-122
0 komentar:
Admin telah menghapus verifikasi kata pada kotak komentar. Dimohon untuk tidak menggunakan kata2 yang berbau SARA, dan mohon menggunakan kata2 yang sopan