How much Do you Like My Blogs

Friday, 2 March 2012

Does Dark Galaxies exist in the Universe?


Authors_:** Mr.Rupak Bhattacharya Bsc(cal) Msc(JU) 7/51 purbapalli, Po-sodepur Dist 24parganas(north) , Kolkata-110,West Bengal, India·         Pranabkumar Bhattacharya MD(cal) FIC Path(ind), Professor and HOD Pathology Calcutta Schhol of Tropical medicine  Ex Prof &HOD Opthalmic Pathology RIO, Kol-73 & of WBUHS,   Ex Professor of pathology, Institute of Post Graduate Medical Education & Research,244 a AJC Bose Road, Kolkata-20,  West Bengal India *Miss Upasana Bhattacharya - Daughter of Professor Pranab kumar Bhattacharya
***Mr. Ritwik Bhattacharya B.com(cal) **Miss Rupsa Bhattacharya of Residence  7/51 purbapalli, Po-sodepur Dist 24 parganas(north) , Kolkata-110,WestBengal, India, *** Miss Oaindrila Mukherjee-Student, ***Mrs Dalia Mukherjee BA(hons) Cal and ***Mr. Debasis Mukherjee Bsc(cal) of Swamiji nagar South Habra 24 parganas(north) West Bengal 


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.RupakBhattacharya, one of the authors of this letter in [www.bautforum.com] of Bad Astronomy & universe Today Forum US in one such Threads “Dark Galaxies”[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 “……… evidence from NASA’s 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………”.  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’s 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.harvard.edu/abs/2005ApJ...622L..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.org/messier/more/virgo.html). Bekki, Koribalski & Kilborn, 2005 (http://adsabs.harvard.edu/abs/2005MNRAS.363L..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.org/messier/m/m099.html). This conclusion was further reinforced by Duc & Bournaud, in 2008 (http://adsabs.harvard.edu/abs/2008ApJ...673..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 “dark galaxy”, but rather a massive tidal debris of gas that cloud produced in the active galaxy cluster. Meanwhile, Davies, et al., 2006 (http://adsabs.harvard.edu/abs/2006MNRAS.368.1479D) pointed out that current HI surveys were not sensitive enough, and did not have the velocity resolution required, to detect as many “dark galaxies” as predicted by cold dark matter models. So we were obliged to await better data and evidence.
Many scientists also suggested that “Dark galaxies” are not actually “galaxies” 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 “dark galaxy”.
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 ‘dark matter’ made up of neutral hydrogen (and perhaps other dust and gas) may be nothing more than ‘dark mass’ 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., ‘dark mass’ which we have come to call ‘dark matter’. The same is present on the periphery of galaxies causing flat rotation curves. Galaxies made up of this ‘high dark mass’ can remain low luminosity, or virtually no luminosity, except
detected by radio waves or gravitational lensing. However, this ‘dark mass’ 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 ‘dark matter’ without further explanation, except it is believed to be ‘exotic’ and non-baryonic matter, which as yet remains illusive and undetected. The presence of neutral hydrogen may be a clue, however.

Colour optical image of VIRGOHI 21 with neutral
hydrogen contours superimposed
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 KumarBhattacharya taken from The threads “Dark Galaxies” of [www.bautforum.com] of BAD astronomy &universe today forum —Preceding 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 “ Thread “ Dark Galaxy” started on 10th January 2008 at astronomy forum on Badastronomyand universe today forum[7 answers-679 views]
Acknowledgement- To the diseased  parents  of Professor Pranab kumar Bhattacharya 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

 one may  click to view following links of publication by the authors on dark galaxy