New calculations suggest Andromeda might not collide with Milky Way

The uncertainty of science: Scientists using new data from the Hubble Space Telescope as well as Europe’s Gaia space telescope, combined with many computer models, have determined that the 2012 prediction that the Andromeda galaxy would collide with Milky Way in five billion years was much more uncertain. From the abstract of the paper:

[W]e consider the latest and most accurate observations by the Gaia and Hubble space telescopes, along with recent consensus mass estimates, to derive possible future scenarios and identify the main sources of uncertainty in the evolution of the Local Group over the next 10 billion years. We found that the next most massive Local Group member galaxies — namely, M33 and the Large Magellanic Cloud—distinctly and radically affect the Milky Way — Andromeda orbit. Although including M33 increases the merger probability, the orbit of the Large Magellanic Cloud runs perpendicular to the Milky Way–Andromeda orbit and makes their merger less probable.

In the full system, we found that uncertainties in the present positions, motions and masses of all galaxies leave room for drastically different outcomes and a probability of close to 50% that there will be no Milky Way–Andromeda merger during the next 10 billion years. Based on the best available data, the fate of our Galaxy is still completely open.

The press release at the first link above makes it sounds as the previous prediction of a collision had been fully accepted as certain by the entire astronomical community, and that is balder-dash. It was simply the best guess at the time, highly uncertain. This new prediction — that we really don’t know what will happen based on the data available — is simply the newest best guess.

This new analysis however is certainly more robust and honest.

The spiral dust streams within the Andromeda galaxy

Andromeda in infrared
Click for original image.

Cool image time! The picture above, cropped and reduced to post here, was released yesterday and uses archival infrared data from the now retired Spitzer Space telescope to highlight the dust found within the Andromeda galaxy, about two million light years away.

Spitzer’s infrared view was similar to Webb’s but at a far lower resolution. In the picture above the red indicates cool dust.

By separating these wavelengths and looking at the dust alone, astronomers can see the galaxy’s “skeleton” — places where gas has coalesced and cooled, sometimes forming dust, creating conditions for stars to form. This view of Andromeda revealed a few surprises. For instance, although it is a spiral galaxy like the Milky Way, Andromeda is dominated by a large dust ring rather than distinct arms circling its center. The images also revealed a secondary hole in one portion of the ring where a dwarf galaxy passed through.

The data also suggested that the dust is flowing at a very steady rate into Andromeda’s central black hole. According to computer simulations, this steady rate would explain why the supermassive black holes at the center of both Andromeda and the Milky Way are relative inactive. If the dust fell in clumps rather than a steady flow, both black holes would exhibit bursts of high activity, similar to active galactic centers.

A side note for anyone wishing to star-gaze: Andromeda is actually the largest visible galaxy in the night sky, about six times with width of the full Moon. If you can get to a very dark-sky location, get your eyes very dark-adapted, and you know where to look, you can actually see it with the naked eye. I did this once at a star party, helped by a bunch of amateur astronomers. The galaxy is very faint, and it helps to use binoculars to help locate it, but once identified its size in the sky truly is breath-taking.

Hubble maps giant gas halo around Andromeda

Astronomers using the Hubble Space Telescope’s ability to observe in ultraviolet wavelengths have now mapped the giant halo of gas that surrounds the Andromeda galaxy 2.5 million light years away.

The work found that the halo appears to have both an inner and outer shell.

“We find the inner shell that extends to about a half million light-years is far more complex and dynamic,” explained study leader Nicolas Lehner of the University of Notre Dame in Indiana. “The outer shell is smoother and hotter. This difference is a likely result from the impact of supernova activity in the galaxy’s disk more directly affecting the inner halo.”

A signature of this activity is the team’s discovery of a large amount of heavy elements in the gaseous halo of Andromeda. Heavier elements are cooked up in the interiors of stars and then ejected into space—sometimes violently as a star dies. The halo is then contaminated with this material from stellar explosions.

The Andromeda galaxy, also known as M31, is a majestic spiral of perhaps as many as 1 trillion stars and comparable in size to our Milky Way. At a distance of 2.5 million light-years, it is so close to us that the galaxy appears as a cigar-shaped smudge of light high in the autumn sky. If its gaseous halo could be viewed with the naked eye, it would be about three times the width of the Big Dipper. This would easily be the biggest feature on the nighttime sky.

Though there is of course uncertainty here, this research is confirming earlier work, making its conclusions more robust.

A side note: Ultraviolet observations can only be done in space, as the atmosphere blocks it. Hubble I think is the only telescope in space right now with this capability. There used to be others, the most noteworthy of all being the International Ultraviolet Explorer, which functioned from 1978 to 1996 but was then decommissioned because neither NASA nor ESA were willing to fund its operation any longer.

No replacements have been launched because the budget for space astronomy has almost entirely been eaten by the overbudget and long delayed James Webb Space Telescope, with future budgets to be eaten similarly by the Roman.Space Telescope.