February 15, 2012
Black Hole Found At The Center Of A Shredded Galaxy
Astronomers say they have found a black hole that was once at the core of a now-disintegrated dwarf galaxy.
The researchers used NASA's Hubble Space Telescope to find a cluster of young, blue stars encircling the first intermediate-mass black hole ever discovered.
"For the first time, we have evidence on the environment, and thus the origin, of this middle-weight black hole," Mathieu Servility, who worked at the Harvard-Smithsonian Center for Astrophysics when this research was conducted, said in a press release.
It is unclear exactly how super massive black holes form in the cores of galaxies. One theory is that they build up through the merger of smaller, intermediate-mass black holes.
Lead author Sean Farrell discovered the black hole in 2009 by using the European Space Agency's XMM-Newton X-ray space telescope.
The black hole weighs in at 20,000 solar masses and lies at the edge of the galaxy ESO 243-49, which is 290 million light-years from Earth.
The astronomers observed the black hole with NASA's Swift observatory in X-ray and Hubble in near-infrared, optical, and ultraviolet wavelengths.
The intensity and the color of the light shows a cluster of young stars, 250 light-years across, encircling the black hole.
The team detected blue light from hot gas in the accretion disk swirling around the black hole. However, they also found the red light was produced by much cooler gas.
Computer models suggested the presence of a young, massive cluster of stars encircling the black hole.
"What we can definitely say with our Hubble data is that we require both emission from an accretion disk and emission from a stellar population to explain the colors we see," Farrell said.
The team said that the black hole was the central black hole in a dwarf galaxy, and the larger host galaxy then captured the dwarf. They believe most of the dwarf's stars were stripped away through the collision between the galaxies.
Also, new your stars were formed in the encounter, and the interactions that compressed the gas around the black hole also triggered star formations.
The team found that the star cluster must be less than 200 million years old, which means the bulk of the stars were formed following the dwarf's collision with the larger galaxy.
"This black hole is unique in that it's the only intermediate-mass black hole we've found so far. Its rarity suggests that these black holes are only visible for a short time," Servillat said.
The findings were published in the February 15 issue of the Astrophysical Journal Letters.
Image Caption: This spectacular edge-on galaxy, called ESO 243-49, is home to an intermediate-mass black hole that may have been stripped off of a cannibalized dwarf galaxy. The estimated 20,000-solar-mass black hole lies above the galactic plane. This is an unlikely place for such a massive back hole to exist, unless it belonged to a small galaxy that was gravitationally torn apart by ESO 243-49. The circle identifies a unique X-ray source that pinpoints the black hole. The X-rays are believed to be radiation from a hot accretion disk around the black hole. The blue light not only comes from the disk, but also from a cluster of hot young stars that formed around the black hole. The galaxy is 290 million light-years from Earth. Hubble can't resolve the stars individually because the suspected cluster is too far away. Their presence is inferred from the color and brightness of the light coming from the black hole's location. Credit: NASA, ESA, and S. Farrell (Sydney Institute for Astronomy, University of Sydney)
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- Hubble Space Telescope (ESA)
- Hubble Space Telescope (NASA)
- Harvard-Smithsonian Center for Astrophysics
- Swift Observatory
- Astrophysical Journal Letters Article