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Astronomers bring Andromeda down to size

Astronomers bring Andromeda do...
New research indicates that the Andromeda galaxy is approximately the same size as the Milky Way
New research indicates that the Andromeda galaxy is approximately the same size as the Milky Way
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With the sizes of the two galaxies now thought to be roughly the same, new simulations are needed to find out what will happen when they eventually collide in around 5 billion years
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With the sizes of the two galaxies now thought to be roughly the same, new simulations are needed to find out what will happen when they eventually collide in around 5 billion years
New research indicates that the Andromeda galaxy is approximately the same size as the Milky Way
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New research indicates that the Andromeda galaxy is approximately the same size as the Milky Way

Our galactic big brother might not be so big after all. Overturning 50 years of thinking on the subject, astronomers at the International Centre for Radio Astronomy Research (ICRAR) in Australia have calculated that the Andromeda galaxy has a similar mass to the Milky Way.

Lying around 2.5 million light-year away, Andromeda is the nearest major galaxy to our own. Astronomers have previously believed it to be two to three times more massive than the Milky Way, but the technique employed by the ICRAR team returned a very different result.

That technique uses observations of fast moving stars within the galaxy to determine the speed at which an object needs to be traveling to escape it (called escape velocity), which is in turn used to calculate the galaxy's mass.

"When a rocket is launched into space, it is thrown out with a speed of 11 km/s to overcome the Earth's gravitational pull," says astrophysicist Dr. Prajwal Kafle, from The University of Western Australia branch of ICRAR. "Our home galaxy, the Milky Way, is over a trillion times heavier than our tiny planet Earth so to escape its gravitational pull we have to launch with a speed of 550 km/s. We used this technique to tie down the mass of Andromeda."

The team concluded that Andromeda is 800 billion times heavier than the Sun – a figure comparable to the mass of the Milky Way.

According to Dr. Kafle, the findings also indicate that the amount of dark matter in the Andromeda galaxy is only a third of that uncovered in previous observations.

With the mass of the two galaxies now thought to be similar, new simulations are needed to find out what will happen when they eventually collide in around 5 billion years.

"We had thought there was one biggest galaxy and our own Milky Way was slightly smaller but that scenario has now completely changed," says Dr Kafle. "It's really exciting that we've been able to come up with a new method and suddenly 50 years of collective understanding of the local group has been turned on its head."

The study was published in the journal Monthly Notices of the Royal Astronomical Society.

Source: International Centre for Radio Astronomy Research (ICRAR)

4 comments
Robert Walther
I would think that the Milky Way is a trillion times +/- heavier than the sun, and our sun is a million times heavier than the Earth. This would make Earth mass one quintillionth +/- the mass of our galaxy. Though I could be off as my bathroom scale doesn't even get my weight correctly.
Bob
This is quite an admission that they have been so far off on their estimates of something so close and well studied in cosmic terms. How many other assumptions have they been wrong about? Things that have been presented to the public as irrefutable facts.
FerrisPoobah
Collide in 5 billion years?!?!? NOW you tell me?
bwana4swahili
Still to be peer reviewed and confirmed! Things change when others look at the data. I wouldn't downgrade Andromeda quite yet!!