What Is The Size Of The Milky Way

Our galaxy is a whole lot bigger than it looks. New work finds that the Galaxy stretches about 2 million light-years across, more than than 15 times wider than its luminous spiral disk. The number could atomic number 82 to a better approximate of how massive the galaxy is and how many other galaxies orbit information technology.

Astronomers take long known that the brightest part of the Milky way, the pancake-shaped deejay of stars that houses the lord's day, is some 120,000 lite-years across (SN: eight/1/xix). Across this stellar disk is a disk of gas. A vast halo of dark matter, presumably full of invisible particles, engulfs both disks and stretches far beyond them (SN: 10/25/16). But considering the dark halo emits no light, its diameter is hard to measure.

At present, Alis Deason, an astrophysicist at Durham University in England, and her colleagues have used nearby galaxies to locate the Milky Style's edge. The precise diameter is one.9 1000000 low-cal-years, give or take 0.iv meg light-years, the team reports February 21 in a newspaper posted at arXiv.org.

To put that size into perspective, imagine a map in which the distance between the sun and the Earth is simply one inch. If the Milky way's heart were at the eye of the Earth, the milky way'southward edge would be 4 times farther away than the moon really is.

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To find the Milky way'southward edge, Deason'south squad conducted reckoner simulations of how behemothic galaxies like the Galaxy class. In item, the scientists sought cases where two giant galaxies arose adjacent, like the Milky Way and Andromeda, our nearest behemothic neighbour, because each galaxy'due south gravity tugs on the other (SN: 5/12/fifteen). The simulations showed that just beyond the edge of a giant milky way'southward dark halo, the velocities of small-scale nearby galaxies drop sharply (SN: 3/11/15).

Using existing telescope observations, Deason and her colleagues found a similar plunge in the speeds of small galaxies near the Milky Way. This occurred at a distance of virtually 950,000 light-years from the Milky Way's centre, marking the galaxy's border, the scientists say. The edge is 35 times farther from the galactic center than the sun is.

Although dark thing makes up most of the Milky Way's mass, the simulations reveal that stars should also exist at these far-out distances. "Both have a well-defined edge," Deason says. "The edge of the stars is very precipitous, almost like the stars just cease at a particular radius."

In the future, astronomers can refine the location of the Milky Way's edge by discovering additional small galaxies nearby. Astronomers could likewise search for individual stars out at the boundary, says Mike Boylan-Kolchin, an astrophysicist at the University of Texas at Austin who was not involved with the study. The farthest such stars will be very dim, just hereafter observations should be able to find them.

The measurement should as well assistance astronomers tease out other galactic properties. For instance, the larger the Milky Way, the more massive it is — and the more galaxies there should be revolving around it, says Rosemary Wyse, an astronomer at Johns Hopkins University who was not part of the new piece of work. So far, there are about 60 known Milky Mode satellites, but astronomers suspect that many more await discovery.