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New Study Pushes Back Milky Way’s Dust-up with Andromeda

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Utilizing knowledge from the Gaia satellite tv for pc, astronomers have dissected the dance of our galactic neighbors, discovering a bunch of insights into how galaxies within the Native Group evolve and work together.

Astronomers have used the European Area Company’s Gaia satellite tv for pc to measure the rotation on the aircraft of the sky for the Andromeda and Triangulum galaxies – the biggest galaxies within the Native Group exterior of the Milky Means. The outcomes have some shocking implications for our future — in four.5 billion years or so.

“We all know galaxies rotate,” says Roeland van der Marel (Area Telescope Science Institute), who led a workforce in publishing the ends in The Astrophysical Journal. However, he provides, this rotation has by no means been measured in three dimensions and on the extent of particular person stars. “However with lower than two years of Gaia knowledge, we have been in a position to measure the 250 million-year revolution of Andromeda.” To place this in perspective, van der Marel says, the celebs that Gaia was watching transfer on the similar pace human hair would develop as seen on the distance of the Moon.

To know the galaxies’ present motions, the researchers used the second knowledge launch from the Gaia satellite tv for pc – which supplies correct distance measurements to an astonishing 1.7 billion stars. The researchers averaged the motions of 1,084 and 1,518 stars in Andromeda and Triangulum, respectively, to calculate each galaxies’ rotation, in addition to their movement throughout the sky.

Rotation of Andromeda Galaxy

A view of the Andromeda galaxy, obtained with NASA’s Galex satellite tv for pc at near-ultraviolet wavelengths, highlights areas inside the galaxy the place stars are forming. Blue symbols mark the areas of vivid younger stars used to measure the movement of the galaxy. Yellow arrows point out the typical stellar motions at numerous areas based mostly on knowledge from Gaia’s second knowledge launch. A counter-clockwise rotation of the spiral galaxy’s disc is obvious.
Star motions: ESA / Gaia; Background picture: NASA / Galex; R. van der Marel / M. Fardal / J. Sahlmann (STScI)

The workforce then simulated previous and future motion of Native Group galaxies throughout the sky, trying billions of years back and forth in time. The projections allowed them to reply two central questions in regards to the Native Group.

When Did the Native Group Come Collectively?

Each the Milky Means and Andromeda have satellite tv for pc galaxies which might be roughly 1/10th their mass – the Giant Magellanic Cloud and the Triangulum Galaxy, respectively. It was beforehand thought that these satellites had been long-term companions of their larger cousins. Nevertheless, more recent work has revealed that the Giant Magellanic Cloud is falling into our galaxy for the very first time. It’s a protracted fall — the 2 gained’t merge for about one other 2.5 billion years.

Sharp photos from the Hubble Area Telescope and radio knowledge from the Very Lengthy Baseline Array had instructed that Andromeda and Triangulum may need had a special historical past: passing shut by one another 6 billion years in the past and are doing so once more presently.

However the brand new simulations reveal that this state of affairs can’t be true — Triangulum is barely now making its first method. Basically, this consequence means that the Native Group got here collectively extra not too long ago than beforehand thought ­– and it’s nonetheless rising at the moment.

Once and Future Galaxies

The long run orbital trajectories of the three largest galaxies within the Native Group: our Milky Means (blue), Andromeda, also referred to as M31 (pink), and Triangulum, also referred to as M33 (inexperienced).
Orbits: E. Patel / G. Besla (Univ. of Arizona) / R. van der Marel (STScI); Photographs: ESA (Milky Means); ESA / Gaia / DPAC (M31, M33)

At a broader degree, the consequence provides to proof that galactic interactions are way more dynamic than anticipated. “It’s a lot much less seemingly galaxy can have a companion that simply hangs round for billions and billions of years, with out merging,” says van der Marel. As a substitute, merging is frequent and occurs comparatively quick.

When Will the Milky Means and Andromeda Galaxies Meet?

The workforce’s evaluation additionally discovered that the Milky Means meet-up with Andromeda gained’t play out the best way we as soon as thought. Astronomers have lengthy recognized that Andromeda is barrelling in direction of us at about 110 km/s. However what has been tougher to gauge is how briskly our sister galaxy is shifting sideways. A big sideways movement may even have Andromeda miss the Milky Means fully.

Van der Marel known as the Hubble Area Telescope into motion in 2012 to reply this query. Hubble knowledge instructed that there was solely a small sideways movement (about 17 km/s), so the 2 galaxies have been heading for a head-on collision. However now, after averaging the Hubble outcomes with the brand new Gaia measurements, van der Marel’s workforce finds that Andromeda is sliding sideways extra rapidly, at round 50 km/s. “Which means the orbit [of the two galaxies] will likely be extra of a glancing blow than a head-on collision,” he says. “Nevertheless it’s nonetheless very a lot the case that these two galaxies will finally collide.”

View of M31 in 3¾ billion years

Billions of years from now, the Andromeda Galaxy will loom massive within the evening sky as its fateful collision with our Milky Means nears.
S.T. Sohn & others / ApJ

The brand new consequence revises the anticipated date of the galactic merger from three.9 billion years’ time to four.5 billion. By then, the Earth will likely be twice its present age and fully uninhabitable. However there’s a slim probability our distant descendants may go to their former residence to observe what’s going to undoubtedly be the best lightshow within the historical past of our nook of the universe.




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