New evidence for a Dark Matter Galaxy

Jan 12, 2006
Dark Galaxy VIRGOHI 21 has no starlight but radio waves from neutral hydrogen betray its existence
Dark Galaxy VIRGOHI 21 has no starlight but radio waves from neutral hydrogen betray its existence. The contours superimposed on this optical image indicate how much gas was detected. This material was presented to the American Astronomical Society meeting in Washington, D. C. on January 12, 2006. CREDIT: Arecibo Observatory / Cardiff University / Isaac Newton Telescope / Westerbork Synthesis Radio Telescope

New evidence that VIRGOHI 21, a mysterious cloud of hydrogen in the Virgo Cluster 50 million light-years from the Earth, is a Dark Galaxy, emitting no star light, was presented today at the American Astronomical Society meeting in Washington, D. C. by an international team led by astronomers from the National Science Foundation’s Arecibo Observatory and from Cardiff University in the United Kingdom. Their results not only indicate the presence of a dark galaxy but also explain the long-standing mystery of its strangely stretched neighbour.

The new observations, made with the Westerbork Synthesis Radio Telescope in the Netherlands, show that the hydrogen gas in VIRGOHI 21 appears to be rotating, implying a dark galaxy with over ten billion times the mass of the Sun. Only one percent of this mass has been detected as neutral hydrogen – the rest appears to be dark matter.

But this is not all that the new data reveal. The results may also solve a long-standing puzzle about another nearby galaxy. NGC 4254 is lopsided, with one spiral arm much larger than the rest. This is usually caused by the influence of a companion galaxy, but none could be found until now – the team thinks VIRGOHI 21 is the culprit. Dr. Robert Minchin of Arecibo Observatory says; “The Dark Galaxy theory explains both the observations of VIRGOHI 21 and the mystery of NGC 4254.”

Neutral hydrogen gas streams between NGC 4254 (top left) and the Dark Galaxy VIRGOHI 21 (center right)
Neutral hydrogen gas streams between NGC 4254 (top left) and the Dark Galaxy VIRGOHI 21 (center right) in this image made from radio telescope observations at a wavelength of 21 centimeters. This interaction could explain the mystery of NGC 4254's peculiar lopsided shape. To the bottom left, a ring of gas can be seen around the galaxy NGC 4262. This material was presented to the American Astronomical Society meeting in Washington, D. C. on January 12, 2006. CREDIT: Arecibo Observatory / Cardiff University / Westerbork Synthesis Radio Telescope

Gas from NGC 4254 is being torn away by the dark galaxy, forming a temporary link between the two and stretching the arm of the spiral galaxy. As the VIRGOH1 21 moves on, the two will separate and NGC 4254’s unusual arm will relax back to match its partner.

The team have looked at many other possible explanations, but have found that only the Dark Galaxy theory can explain all of the observations. As Professor Mike Disney of Cardiff University puts it, “The new observations make it even harder to escape the conclusion that VIRGOHI 21 is a Dark Galaxy.”

The team hope that this will be the first of many such finds. “We’re going to be searching for more Dark Galaxies with the new ALFA instrument at Arecibo Observatory,” explains Dr. Jon Davies of Cardiff University. “We hope to find many more over the next few years – this is a very exciting time!”

Source: PPARC

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Bapi
1 / 5 (1) Aug 09, 2009
Title-: Does Dark Galaxies exist in the Universe?
Authors_:** Mr. Rupak Bhattacharya Bsc(cal) Msc(JU) 7/51 purbapalli, Po-sodepur Dist 24 parganas(north) , Kolkata-110,West Bengal, India
%u2022Pranab kumar Bhattacharya MD(cal) FIC Path(ind), Professor of pathology, Institute of Post Graduate Medical Education & Research,244 a AJC Bose Road, Kolkata-20, West Bengal India
***Mr. Ritwik Bhattacharya B.com(cal) 7/51 purbapalli, Po-sodepur Dist 24 parganas(north) , Kolkata-110,WestBengal, India
**** Dr. Avisnata Das MBBS(cal)
*****Miss Upasana Bhattacharya
www.unipathos.com

Is there any Dark Galaxies in our observable universe? If they are present what are they? Of what matter they were formed? How to detect those Dark galaxies in the universe? Such few important questions once were placed for discussion by Mr.Rupak Bhattacharya, one of the authors of this letter in [www.bautforum.com]www.bautforum.com[/url]] of Bad Astronomy & universe Today Forum US in one such Threads %u201CDark Galaxies%u201D[2]. These questions were probably associated with understanding how did our universe really blossomed from the Big Bang origin. According to increasingly refined story of universe creation 85% of the matter in the visible universe is not ordinary baryonic matter-that made up galaxies and stars and planets. Rather it is the dark matter. As the universe grew from its infancy, the dark matter condensed in to enormous filaments like structures strings, tubes, clumps and haloes. These weighty objects were pooled in hydrogen gas which formed the galaxies and stars. Simulations show that dark matter should have myriad clumps between 1/1000 and 1/1000,000 as massive as our own milky way galaxy. At first these small haloes should have accumulated gas and lit up as small dwarf galaxies, thousands of which should whiz around the Milky Way. So far, astronomy could have few near by also. Various factors kept the small halos dark. So space time should have many such dark galaxies. They are all invisible galaxies. Not even the power of Hubble telescope has been able to see any stars within it. VIRGO HI -21, an intergalactic gas cloud 50 million light-years approximately from the Earth. An international team of astronomers found that it was rotating like an ordinary galaxy but without any starlight shining out, making it a coveted dark galaxy.
According to the paper published said %u201C%u2026%u2026%u2026 evidence from NASA%u2019s Hubble Space Telescope and the Westerbork Synthesis Radio Telescope in the Netherlands had been used to rule out all but one of the ideas put forward to explain the existence of VIRGOHI 21, an intergalactic gas cloud 50 million light-years from the Earth%u2026%u2026%u2026%u201D. and the paper concluded that an international team of astronomers found that it was rotating like an ordinary galaxy but without any starlight shining out, making it a coveted dark galaxy. VIRGO HI 21, was in fact a mysterious cloud of hydrogen in the Virgo Cluster, 50 million light-years from the Earth, is considered a Dark Galaxy, emitting no star light, was however presented at the American Astronomical Society meeting in Washington, D. C. by an international team led by astronomers from the National Science Foundation%u2019s Arecibo Observatory and from Cardiff University in the United Kingdom in 2005. Their results then not only indicated presence of a dark galaxy but also explained the long-standing mystery of its strangely stretched neighbor NGC 4254. So far knowledge of authors VIRGOHI21 was first described by Minchin, et al.in 2005 (http://adsabs.har...L..21M). Even in that first paper the authors pointed out that the object could be a massive HI cloud trapped in the gravity well of a dark matter cluster, or it could be simple tidal debris from interacting galaxies in the Virgo cluster. (http://www.seds.o...o.html). Bekki, Koribalski & Kilborn, 2005 (http://adsabs.har...3L..21B) numerically modeled HI tidal debris in the Virgo environment and concluded that VIRGOHI21 is most likely tidal debris associated with M99 (NGC 4254) (http://www.seds.o...9.html). This conclusion was further reinforced by Duc & Bournaud, in 2008 (http://adsabs.har.....787D), who were able to reproduce the details of the shape & kinematics of VIRGO HI21 as tidal debris associated with NGC 4254. At this point the weight of evidence however showed that VIRGOHI21 is likely not a %u201Cdark galaxy%u201D, but rather a massive tidal debris of gas that cloud produced in the active galaxy cluster. Meanwhile, Davies, et al., 2006 (http://adsabs.har...8.1479D) pointed out that current HI surveys were not sensitive enough, and did not have the velocity resolution required, to detect as many %u201Cdark galaxies%u201D as predicted by cold dark matter models. So we were obliged to await better data and evidence.
Many scientists also suggested that %u201CDark galaxies%u201D are not actually %u201Cgalaxies%u201D in any common sense of the word. The expectation was that there should be dark matter concentrations into which normal gas fell, but not enough to form stars, or any kind of galactic objects. Hence, a lonely cloud
of neutral hydrogen gas (HI) would be expected, VIRGOHI21 being a possible example. But since, such objects could also form as tidal debris, especially in a dynamic environment like the Virgo cluster, where galaxy interactions are expected, one must first show that tidal debris is an unreliable option, before drawing the more exotic conclusion of %u201Cdark galaxy%u201D.
But the fact is there is actually one suspected in the Virgo Cluster of galaxies are dark Galaxies. It must be obviously invisible to the visible light, but it is of course visible to radio frequencies that can detect neutral hydrogen. It is believed that dark galaxies such as it consist of dark matter and small amounts of hydrogen gas. Having lots of dark matter is not unusual, most if not all galaxies consist mostly of it, but for some reason star birth does not start in such galaxies. And why not?
Dark galaxies if found are today in fact evidences for the existence of dark matter .It may be that %u2018dark matter%u2019 made up of neutral hydrogen (and perhaps other dust and gas) may be nothing more than %u2018dark mass%u2019 of the same matter detected in such small amounts. This would translate into the detected dark gas, such as neutral hydrogen, responsive to radio but not visible light, is very diffuse matter of a much higher gravity G factor. This high G renders the matter gravitationally observable as high mass, i.e., %u2018dark mass%u2019 which we have come to call %u2018dark matter%u2019. The same is present on the periphery of galaxies causing flat rotation curves. Galaxies made up of this %u2018high dark mass%u2019 can remain low luminosity, or virtually no luminosity, except detected by radio waves or gravitational lensing. However, this %u2018dark mass%u2019 idea is not current in modern cosmology, and would need to be tested further if it is to form a working hypothesis. For now, it is merely known as %u2018dark matter%u2019 without further explanation, except it is believed to be %u2018exotic%u2019 and non-baryonic matter, which as yet remains illusive and undetected. The presence of neutral hydrogen may be a clue, however.


Dark galaxies picture; the dark galaxy VIRGOHI 21 has no starlight, but radio waves from neutral hydrogen gas betray its existence[from R. Minchin / Arecibo Observatory / Cardiff University / Isaac Newton Telescope / Westerbork Synthesis Radio Telescope]
References
1].From Wikipedia: user page : talk BapiPatho Does Dark Galaxies Exist?
Professor Pranab Kumar Bhattacharya taken from The threads %u201CDark Galaxies%u201D of [www.bautforum.com]www.bautforum.com[/url]] of BAD astronomy &universe today forum %u2014Preceding unsigned comment added by 210.212.2.201 (talk) 12:49, 6 May 2008 (UTC) modified on 4 November 2008,
2 ] Professor Pranab Kumar Bhattacharya, Rupak Bhattacharya, Ritwik Bhattacharya and Miss Upasana Bhattacharya %u201C Thread %u201C Dark Galaxy%u201D started on 10th January 2008 at astronomy forum on Badastronomyand universe today forum[7 answers-679 views]
Acknowledgement- To recently diseased late Mr. Bholanath Bhattacharya and Mrs late Bani Bhattacharya of7/51 purbapalli, Po-sodepur Dist 24 parganas(north) , Kolkata-110,WestBengal, India
Copy Right- Strictly reserved to Professor Pranab Kumar Bhattacharya as per IPR copy Right Rules

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