New evidence that VIRGOHI 21, a mysterious cloud of hydrogen in the Virgo cluster, 21 million light years from Earth, is a dark galaxy that does not emit starlight.
Avi Blizovsky
New evidence that VIRGOHI 21, a mysterious cloud of hydrogen in the Virgo cluster, 21 million light years from Earth, is a dark galaxy that does not emit starlight. This was presented at the meeting of the American Astronomical Union in Washington, by a team of astronomers from Arecibo Observatory and Cardiff University in the UK.
The findings of the American-British group not only indicate the existence of a dark galaxy but also provide an explanation for the long-standing mystery of the elongated neighboring galaxy phenomenon.
The new observation made with a radio telescope in the Netherlands showed that the hydrogen gas in Virgo 21 appears to be rotating, which means that there is a dark galaxy there that melts tens of millions of times the mass of the Sun. Only one percent of this mass was discovered to be neutral gas - and the rest appeared to be dark matter.
However, this is not all the information revealed. The result may also solve a long-standing puzzle about a neighboring galaxy. NGC 4254 is a barred galaxy with one spiral arm much larger than the rest. This phenomenon is caused by the influence of the gravitational force of a neighboring galaxy, but this has not been found so far. The team believes that Virgo 21 is to blame. Dr. Robert Minchin of the Arecibo Observatory says: "The dark galaxy theory explains the two observations - both of Virgo 21 and of NGC 4254.
The gas from NGC 4254 is torn apart by the dark galaxy, temporarily connecting the two and stretching the arm of the spiral galaxy. As Virgo 21 continues, the two will separate and the arm will return to resemble its members.
The team also looked at many other explanations, but found that only the dark galaxy theory could explain all the observations. Prof. Mike Disney from Cardiff University says: "The new observations make it even more difficult for astronomers to escape the conclusion that Virgo 21 is a dark galaxy.
Team members hope that the find will be the first of many. "We are going to scan the sky for similar galaxies using the ALFA facility in Arecibo," explains Dr. John Davies of Cardiff. "We hope to find many more galaxies over the next two years. This is an exciting moment." Concluded.
