Indian-origin astronomer theorises that Milky Way could have a hidden twin

December 1st, 2007 - 12:58 pm ICT by admin  

London, Dec 1 (ANI): A team of astronomers including an Indian born scientist have hinted at the possibility of the Milky Way galaxy having a twin, based on data from the 2 Micron Redshift Survey (2MRS), which aims to map the distribution of galaxies and dark matter in the local universe.
The research pointed towards a new galaxy lurking behind a veil of dust at the centre of the Milky Way, which could be as massive as the Andromeda galaxy.
The huge size of this galaxy could explain the mysterious gravitational pull on the Milky Way.
Astronomers know both the direction and speed of the Milky Way’s motion based on measurements of the cosmic microwave background, which means the radiation that filled all space shortly after the Big Bang. The wavelength of this radiation appears slightly shorter in the direction of the Milky Way’s motion because of the Doppler Effect.
This motion is thought to be due to the gravitational pull from surrounding galaxies and clusters of galaxies. But when the influence of all known galaxies and galaxy clusters is added up, the Milky Way’s actual motion is off by about 20deg.
Now, new calculations suggest that the inconsistency may be due to a large galaxy hidden right on our cosmic doorstep, or a hidden cluster of galaxies somewhat farther away in the same direction.
The calculations, made by Avi Loeb and Ramesh Narayan of the Harvard-Smithsonian Center for Astrophysics in Cambridge, Massachusetts, US, used data from the 2 Micron Redshift Survey (2MRS) to calculate how the Milky Way should be moving if it were affected only by the galaxies observed in that survey. Then they compared that to how our galaxy actually is moving based on measurements of the cosmic microwave background.
They found that our galaxy has an extra motion of 120 kilometres per second in roughly the direction of our galaxy’s centre as seen from Earth.
They found that a galaxy slightly more massive than our own could account for the motion if it were located about 3 million light years away behind our galaxy’s centre. This would make it our most massive neighbour, aside from the Andromeda galaxy, which has a similar mass and is about 2.5 million light years from Earth.
According to the researchers, such a large, nearby galaxy could have remained hidden until now because of the thick dust that obscures the sky in the direction of the galactic centre.
“Another possibility is that the extra pull is due to a large cluster of thousands of galaxies lying about 70 million light years from Earth in the same direction and obscured for the same reason,” said Loeb. “Alternatively, a combination of individual galaxies and galaxy clusters in this direction could be responsible,” he added.
“We are ignorant about our immediate neighbourhood behind the Milky Way,” Loeb told New Scientist. “If we wait 100 million years, the Sun will go to the other side of the galaxy and then we can see what’s on the other side. But that’s a long time to wait and we want to know before that,” he added.
“Radio surveys could penetrate the dust and reveal galaxies behind the galaxy’s centre,” said Loeb.
“There could be a nearby spiral or even a mid-sized elliptical galaxy, which are generally much bigger, within say 10deg of the galactic centre that we do not know about,” said Pirin Erdogdu of Nottingham University in the UK. (ANI)

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