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Distance Estimate: 160 million light yearsX-ray and Optical Images of NGC 3393
The diffuse blue emission in the large image is from hot gas near the center of NGC 3393 and shows low energy X-rays. The inset shows only high energy X-rays, including emission from iron. This type of emission is a characteristic feature of growing black holes that are heavily obscured by dust and gas.
Two separate peaks of X-ray emission (roughly at 11 o'clock and 4 o'clock) can clearly be seen in the inset box. These two sources are black holes that are actively growing, generating X-ray emission as gas falls towards the black holes and becomes hotter. The obscured regions around both black holes block the copious amounts of optical and ultraviolet light produced by infalling material.
Dubbed "minor mergers" by scientists, such collisions of one larger and another smaller galaxy may, in fact, be the most common way for black hole pairs to form. Until the latest Chandra observations of NGC 3393, however, it has has been difficult to find good candidates for minor mergers because the merged galaxy is expected to look like an ordinary spiral galaxy.
If this was a minor merger, the black hole in the smaller galaxy should have had a smaller mass than the other black hole before their host galaxies started to collide. Good estimates of the masses of both black holes are not yet available to test this idea, although the observations do show that both black holes are more massive than about a million Suns.
Fast Facts for NGC 3393:
Coordinates: (J2000) RA 10h 48m 23.40s | Dec -25° 09' 43.00''
Observation Date: 28 Feb. 2004 & 12 March 2011
Observation Time: 27 hours 43 min (1 day 3 hours 43 min).
Obs. ID: 4868, 12290 Color Code: X-ray: Blue; Optical: Gold
References: G.Fabbiano et al, 2011, Nature
Distance Estimate 160 million light years