Astrophysicists from Durham University finds Edge of Milkyway

Keeping aside the vast universe that we look upto exploring in the future years, let us grab a look at our own galaxy, the Milky Way Galaxy. As time rolls , new revelations come up. A team of Astrophysicists From Durham University, England claim to have estimated the actual span of the Milky Way Galaxy. 

New research reveals that the Milky Way spans almost two million light-years, more than fifteen times wider than its luminous spiral disc. The number may result in a better estimate of how massive the galaxy is, and how many other galaxies it orbits.

Astronomers have long known that the brightest part of the Milky Way, the pancake-shaped star disk housing the sun, spans about 120,000 light-years (SN: 8/1/19). There is a disc of gas beyond this stellar disk. A vast halo of dark matter, supposedly full of invisible particles, encompasses both disks and extends far beyond them (SN: 10/25/16). But since the dark halo doesn’t emit light, its diameter is difficult to measure.

(Image Courtesy: NASA; as taken from Hubble Telescope)

Now, Alis Deason, an astrophysicist at Durham University in England, and her colleagues have used galaxies near to locate the edge of the Milky Way. The accurate diameter is 1.9 million light-years, 0.4 million light-years are given or taken, the team reports February 21 in a paper posted on arXiv.org. Read the full Report Here

Imagine a map in which the distance between the sun and the earth is only one inch, to put that size into perspective. If the heart of the Milky Way were at the centre of the Earth, the edge of the galaxy would be four times more distant than the moon actually is.

To find the edge of the Milky Way, Deason’s team conducted computer simulations of how giant galaxies such as the Milky Way formed. Scientists in particular sought cases where two giant galaxies arose side side, such as the Milky Way and Andromeda, our closest giant neighbour, because of the gravity of each galaxy tugs on the other (SN: 5/12/15). The simulations showed that the velocities of tiny near galaxies drop sharply just beyond the edge of the dark halo of a giant galaxy (SN: 3/11/15).

Deason and her colleagues found a similar plunge in the velocities of small galaxies near the Milky Way, using existing telescope observations. This happened at a distance of about 950,000 light-years from the centre of the Milky Way, marking the edge of the galaxy, the scientists say. The edge is 35 times the sun’s distance from the galactic centre.

Although dark matter constitutes most of the mass of the Milky Way, the simulations reveal that stars should also exist at these far-off distances. “There is a well-defined edge for both,” says Deason. “The star edge is very sharp, almost like the stars just stop at a given radius.”

Astronomers may in the future refine the location of the edge of the Milky Way discovering additional small galaxies near. Astronomers were also able to search out at the boundary for individual stars, says Mike Boylan-Kolchin, an astrophysicist at Austin’s Texas University who was not involved in the study. The farthest such stars will be very dim but they should be found future observations.

The measurement should also help tease out other galactic properties for astronomers. The larger the Milky Way, for example, the more massive it is — and the more galaxies it should revolve around, says Rosemary Wyse, an astronomer at Johns Hopkins University who was not part of the new work. There are around 60 known satellites on the Milky Way so far, but astronomers suspect that many more are awaiting discovery.

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