NGC 6240

NGC 6240
Hubble Space Telescope image.
Observation data (J2000 epoch)
Constellation	Ophiuchus
Right ascension	16h 52m 58.9s[1]
Declination	+02° 24′ 03″[1]
Redshift	7339 ± 9 km/s[1]
Distance	400 Mly
Type	I0 pec[1]
Apparent dimensions (V)	2′.1 × 1′.1[1]
Apparent magnitude (V)	12.8[1]
Notable features	merger remnant
Other designations
IC 4625,[1] UGC 10592,[1] PGC 59186,[1] VV 617[1]
See also: Galaxy, List of galaxies

NGC 6240 is a well-studied nearby ultraluminous infrared galaxy (ULIRG) in the constellation Ophiuchus. The galaxy is the remnant of a merger between two smaller galaxies. The collision between the two progenitor galaxies has resulted in a single larger galaxy with two distinct nuclei and a highly disturbed structure, including faint extensions and loops.^[2]

Double Nuclei

Star formation versus supermassive black holes

The power sources of ULIRGs in general has been greatly debated. Infrared light from galaxies generally originates from dust in the interstellar medium. ULIRGs are notable in that they are abnormally bright in the infrared. The infrared dust emission in ULIRGs is over one trillion times more luminous than the Sun (i.e. it has an infrared luminosity of 10¹² L_☉). Astronomers have speculated that either intense star formation regions or active galactic nuclei (which contain supermassive black holes) may be responsible for the intense dust heating that produces this emission, although the general consensus is that both may be present in most ULIRGs. Studying the exact nature of ULIRGs has been difficult, however, because the dust in the centers of these galaxies obscures both visible and near-infrared starlight and because theoretical models of both starbursts and active galactic nuclei have demonstrated that they may look similar. Because NGC 6240 is a nearby example of such a ULIRG, astronomers have studied it intensively to understand its power source.

X-Ray Observations

X-ray image of NGC 6240 taken with the Chandra X-Ray Observatory, superimposed on an optical image of the galaxy. The X-ray emission from the two active galactic nuclei can be seen as bright blue point sources. Credit: NASA.

Observations performed by Stefanie Komossa and collaborators with the Chandra X-Ray Observatory have detected strong hard X-ray emission from both of the nuclei. The intensity of this emission and the presence of emission from lowly ionized or neutral iron indicate that both of the nuclei are active galactic nuclei.^[3] Presumably, these are the black holes that were originally at the centers of the two merging galaxies. Over the course of millions of years, the two black holes are expected to come closer together and form a binary supermassive black hole.

Arp 148, VV 340, Arp 256, NGC 6670, NGC 6240, ESO 593-8, NGC 454, UGC 8335, NGC 6786, NGC 17, ESO 77-14, NGC 6050

See also

• Arp 220 - another ultraluminous infrared galaxy and merger remnant
• Antennae Galaxies - a nearby pair of merging galaxies
• NGC 520 - another merger remnant

References

1. ^ ^{a b c d e f g h i j} "NASA/IPAC Extragalactic Database". Results for NGC 6240. http://nedwww.ipac.caltech.edu/. Retrieved 2006-08-16. 
2. ^ J. W. Fried, H. Schulz (1983). "NGC 6240 - A unique interacting galaxy". Astronomy and Astrophysics 118: 166–170. Bibcode 1983A&A...118..166F. 
3. ^ S. Komossa, V. Burwitz, G. Hasinger, P.Predehl, J. S. Kaastra, Y. Ikebe (2003). "Discovery of a Binary Active Galactic Nucleus in the Ultraluminous Infrared Galaxy NGC 6240 Using Chandra". Astrophysical Journal 582 (1): L15–L19. arXiv:astro-ph/0212099. Bibcode 2003ApJ...582L..15K. doi:10.1086/346145. 

• Chandra: Two Supermassive Black Holes in Same Galaxy