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NGC 3115

NGC 3115

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NGC 3115 is a lenticular (S0) galaxy
Lenticular galaxy
A lenticular galaxy is a type of galaxy which is intermediate between an elliptical galaxy and a spiral galaxy in galaxy morphological classification schemes. Lenticular galaxies are disk galaxies which have used up or lost most of their interstellar matter and therefore have very little ongoing...

 in the constellation
Constellation
In modern astronomy, a constellation is an internationally defined area of the celestial sphere. These areas are grouped around asterisms, patterns formed by prominent stars within apparent proximity to one another on Earth's night sky....

 Sextans. The galaxy was discovered by William Herschel
William Herschel
Sir Frederick William Herschel, KH, FRS, German: Friedrich Wilhelm Herschel was a German-born British astronomer, technical expert, and composer. Born in Hanover, Wilhelm first followed his father into the Military Band of Hanover, but emigrated to Britain at age 19...

 on February 22, 1787. At about 32 million light-years away from us it is several times bigger than our Milky Way
Milky Way
The Milky Way is the galaxy that contains the Solar System. This name derives from its appearance as a dim un-resolved "milky" glowing band arching across the night sky...

. It is a lenticular (S0) galaxy
Lenticular galaxy
A lenticular galaxy is a type of galaxy which is intermediate between an elliptical galaxy and a spiral galaxy in galaxy morphological classification schemes. Lenticular galaxies are disk galaxies which have used up or lost most of their interstellar matter and therefore have very little ongoing...

 because it contains a disk and a central bulge of stars, but without a detectable spiral pattern. NGC 3115 is seen almost exactly edge-on that it was occasionally mis-classified as elliptical. There is some speculation that NGC 3115, in its youth, was a quasar.

Star formation


NGC 3115 has consumed most of the gas of its youthful accretion disk. It has very little gas and dust left that would trigger new star formation. The vast majority of its component stars are very old.

Black hole


In 1992 John Kormendy of the University of Hawaii
University of Hawaii
The University of Hawaii System, formally the University of Hawaii and popularly known as UH, is a public, co-educational college and university system that confers associate, bachelor, master, and doctoral degrees through three university campuses, seven community college campuses, an employment...

 and Douglas Richstone of the University of Michigan
University of Michigan
The University of Michigan is a public research university located in Ann Arbor, Michigan in the United States. It is the state's oldest university and the flagship campus of the University of Michigan...

 announced what was observed to be a supermassive black hole
Supermassive black hole
A supermassive black hole is the largest type of black hole in a galaxy, in the order of hundreds of thousands to billions of solar masses. Most, and possibly all galaxies, including the Milky Way, are believed to contain supermassive black holes at their centers.Supermassive black holes have...

 in the galaxy. Based on orbital velocities of the stars in its core, the central black hole has mass measured to be approximately one billion solar masses. The galaxy appears to have mostly old star
Star
A star is a massive, luminous sphere of plasma held together by gravity. At the end of its lifetime, a star can also contain a proportion of degenerate matter. The nearest star to Earth is the Sun, which is the source of most of the energy on Earth...

s and little or no activity. The growth of its black hole
Black hole
A black hole is a region of spacetime from which nothing, not even light, can escape. The theory of general relativity predicts that a sufficiently compact mass will deform spacetime to form a black hole. Around a black hole there is a mathematically defined surface called an event horizon that...

 has also stopped.

In 2011, NASA's Chandra X-ray Observatory examined the black hole at the center of the large galaxy. A flow of hot gas toward the supermassive black hole has been imaged that for the first time clear evidence for such a flow has been observed in any black hole. As gas flows toward the black hole, it becomes hotter and brighter.
The researchers found the rise in gas temperature begins at about 700 light years from the black hole, giving the location of the Bondi radius. This suggests that the black hole in the center of NGC 3115 has a mass of about two billion times that of the Sun, supporting previous results from optical observations. This would make NGC 3115 the nearest billion-solar-mass black hole to Earth.

See also

  • NGC 5866
    NGC 5866
    NGC 5866 is a relatively bright lenticular or spiral galaxy in the constellation Draco. NGC 5866 was probably discovered by Pierre M├ęchain or Charles Messier in 1781, and independently found by William Herschel in 1788.-Dust disk:One of the most outstanding features of NGC 5866 is the extended...

    - another lenticular galaxy sometimes referred to as the Spindle Galaxy

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