NGC 6240
Template:Short description Template:Sky Template:Infobox Galaxy
NGC 6240, also known as the Starfish Galaxy, is a nearby ultraluminous infrared galaxy (ULIRG) in the constellation Ophiuchus. It was discovered by French astronomer Édouard Stephan on 12 July 1871.<ref name="selig">{{#invoke:citation/CS1|citation |CitationClass=web }}</ref>
The galaxy is the remnant of a merger between three smaller galaxies. The collision between the three progenitor galaxies has resulted in a single, larger galaxy with three distinct nuclei and a highly disturbed structure, including faint extensions and loops.<ref name="friedschulz1983"> Template:Cite journal</ref>
Double nucleiEdit
Star formation versus supermassive black holesEdit
{{ safesubst:#invoke:Unsubst||date=__DATE__ |$B= {{ safesubst:#invoke:Unsubst||date=__DATE__ |$B= Template:Ambox }} }} 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 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 Template:Solar luminosity). 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.Template:Citation needed
X-ray observationsEdit
Observations performed by Stefanie Komossa and collaborators with the Chandra X-Ray Observatory have detected strong hard X-ray emission from two of the nuclei. The intensity of this emission and the presence of emission from lowly ionized or neutral iron indicate that both of these nuclei are active galactic nuclei.<ref name="komossaetal2003"> Template:Cite journal</ref> Presumably, these are the black holes that were originally at the centers of the merging galaxies. Over the course of millions of years, the black holes are expected to come closer together and form a binary supermassive black hole.Template:Citation needed
Recent studies by Wolfram Kollatschny and collaborators using the MUSE instrument on board the VLT have revealed that there are in fact three, not two, supermassive black holes at the core of this remnant. Their masses are suggested to be 90 million, 710 million, and 360 million solar masses.<ref name="kollatschny2020">Template:Cite Q</ref> Two of the three black holes are active. The additional SMBH implies that three original galaxies are merging instead of two.
SupernovaeEdit
Four supernovae have been observed in NGC 6240:
- SN 2000bg ([[Type II supernova#Type_IIn_supernovae|typeTemplate:NbspIIn]], mag. 17.4) was discovered by the Lick Observatory Supernova Search (LOSS) on 1 April 2000.<ref>Template:Cite journal</ref><ref>{{#invoke:citation/CS1|citation
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- SN 2010gp (type Ia, mag. 17.5) was discovered by The CHilean Automatic Supernova sEarch (CHASE) on 14 July 2010.<ref>Template:Cite journal</ref><ref>{{#invoke:citation/CS1|citation
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- SN 2013dc (type II-P, mag. 18.7) was discovered by Adam Block on 11 April 2013.<ref>Template:Cite journal</ref><ref>{{#invoke:citation/CS1|citation
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- PSN J16525760+0223367 (type Ia, mag. 15.8) was discovered by Robert Gagliano, Jack Newton, and Tim Puckett on 23 April 2014.<ref>Bright Supernovae – 2014 Retrieved 25 March 2023.</ref>
Final stagesEdit
A galaxy merger is a slow process lasting more than a billion years as two galaxies, under the inexorable pull of gravity, dance toward each other before finally joining together. After research done over the past few years, scientists have concluded that this galaxy has reached its last stages before colliding into one another. Photographic evidence proves that the two nuclei have been growing closer, and in that process, they have been emitting more gasses and stellar winds outward. Those winds evict about 100 solar masses in gases from the galaxy every year. This type of winds and growth of the black holes are known to occur during the last 10 to 20 million years of the merger; it is assumed that this is the amount of time left for the galaxy to finish its collision phase. <ref>Template:Cite news</ref> After this phase, the merged galaxies will become one, becoming a post-merger object until if and when any tidal tails and plumes evaporate.
GalleryEdit
- Hubble and Keck observatories uncover black holes coalescing.tif
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- Iotw2342c.tiff
NGC 6240 imaged by the Cerro Tololo Inter-American Observatory
See alsoEdit
- Arp 220 – another ultraluminous infrared galaxy and merger remnant
- Antennae Galaxies – a nearby pair of merging galaxies
- NGC 520 – another merger remnant
- Markarian 273 – an ultraluminous infrared galaxy with two active nuclei
- UGC 5101 – another ultraluminous infrared galaxy with active nucleus