Image Credit & Copyright: NASA/ESA Hubble Space Telescope.
150 million light years away lies the remains of a cosmic murder. It appears that as we see it, NGC 922 here was (Cue the Bon Jovi music) shot through the heart some 330 million years ago, killing the spiral galaxy that it once was.
So what do we have for clues here? Well for starters the galaxy is now a ring galaxy with its core now destroyed and vast circular ripples radiating through the structure like ripples from dropping a rock in water. We also have vast regions of star formation created by the shockwave of material as it distorts and compresses the gas and dust that were once spiral arms. As they come to life, the telltale pink hue of star forming nebulae dominates the area.
It’s been observed by the Chandra X-ray telescope that this galaxy also contains at least a couple handful of stellar mass black holes upwards of ten solar masses; at least seven of which are currently feeding.
What about clues as to how this ring galaxy looks as it’s not exactly an obvious ring. If the aggressor punched through the nucleus of this galaxy face on the ring structure would likely be more defined. That means that this collision, even though it passes through the nucleus, was at a steep angle which disturbed the galaxy in a much different way.
So we have the galaxy, its shape and classification, star formation, stellar mass black holes and by the state of things and knowing how long things take to progress all over the universe we should be able to trace, like blood spatter, the culprit that created this mess.
Well it turns out they have and its name is 2MASXI J0224301-244443 and in wide field images of this region it can still be seen speeding away from the scene.
Of course the personification of this galaxy is just being used as an example to illustrate how astronomers, like forensic detectives, have to comb through objects like these very carefully to determine what they’re looking at. Timelines, formations, actions, different wavelength observations, comparisons to like objects seen in previous cases etc. and as new means to investigate are brought to bear, they can even go back and someday solve some current cosmic cold cases.
NAME: NGC 922.
WHAT IS IT?: Ring galaxy and former galaxy involved in a collision where 330 million years ago a smaller galaxy pierced its heart.
HOW BIG IS IT?: 75,000 light years in diameter.
HOW FAR AWAY IS IT?: 150 million light years.
APPARENT MAGNITUDE: 12 (very dim).
WHERE IS IT? (General): Constellation Fornax.
WHERE IS IT? (Exact RA/DEC J2000): RA 02h 25m 04.40s / Dec -24° 47′ 17.00″.
ESA Space Telescope page for this image: http://www.spacetelescope.org/news/heic1218/