For years, astronomers have predicted a dramatic destiny for our galaxy: a head-on collision with Andromeda, our nearest massive galactic neighbour. This merger – anticipated in about 5 billion years – has develop into a staple of astronomy documentaries, textbooks and common science writing.
However in our new examine printed in Nature Astronomy, led by Until Sawala from the College of Helsinki, we discover the Milky Means’s future may not be as sure beforehand assumed.
By fastidiously accounting for uncertainties in current measurements, and together with the gravitational affect of different close by galaxies, we discovered there’s solely a few 50% probability the Milky Means and Andromeda will merge within the subsequent 10 billion years.
Why did we expect a collision was inevitable?
The concept that the Milky Means and Andromeda are on a collision course goes again greater than a century. Astronomers found Andromeda is shifting towards us by measuring its radial velocity – its movement alongside our line of sight – utilizing a slight change within the color of its mild known as the Doppler shift.
However galaxies additionally drift sideways throughout the sky, a motion generally known as correct movement or transverse velocity. This sideways movement is extremely troublesome to detect, particularly for galaxies thousands and thousands of sunshine years away.
Earlier research typically assumed Andromeda’s transverse movement was small, making a future head-on collision appear virtually sure.
What’s completely different on this examine?
Our examine didn’t have any new knowledge. As an alternative, we took a recent have a look at current observations from the Hubble Area Telescope and the Gaia mission.
In contrast to earlier research, our work incorporates the uncertainty in these measurements, reasonably than assuming their most definitely values.
We simulated hundreds of potential trajectories for the Milky Means and Andromeda trajectories, barely various the assumed preliminary situations – issues such because the velocity and place of the 2 galaxies – every time.
Once we began from the identical assumptions the sooner research made, we recovered the identical outcomes. Nonetheless, we have been additionally capable of discover a bigger vary or potentialities.
We additionally included two extra galaxies that affect the longer term paths of the Milky Means and Andromeda: the Giant Magellanic Cloud, an enormous satellite tv for pc galaxy presently falling into the Milky Means, and M33, also referred to as the Triangulum Galaxy, which orbits Andromeda.
The brand new examine took into consideration the gravitational impact of the Triangulum Galaxy, which orbits Andromeda.
ESO, CC BY
These companion galaxies exert gravitational tugs that change the motions of their hosts.
M33 nudges Andromeda barely towards the Milky Means, growing the possibility of a merger. In the meantime, the Giant Magellanic Cloud shifts the Milky Means’s movement away from Andromeda, lowering the chance of a collision.
Taking all of this into consideration, we discovered that in about half of the simulated situations, the Milky Means and Andromeda don’t merge in any respect inside the subsequent 10 billion years.
What occurs in the event that they do – or don’t – collide?
Even when a merger does occur, it’s unlikely to be catastrophic for Earth. Stars in galaxies are separated by huge distances, so direct collisions are uncommon.
However over time, the galaxies would coalesce beneath gravity, forming a single, bigger galaxy – in all probability an elliptical one, reasonably than the spirals we see immediately.
If the galaxies don’t merge, they could settle into an extended, gradual orbit round one another – shut companions that by no means fairly collide. It’s a gentler end result, however it nonetheless reshapes our understanding of the Milky Means’s distant future.
Different galaxies present examples of three future situations for the Milky Means and Andromeda: galaxies passing within the evening, a detailed encounter, a full collision and merger.
NASA / ESA
What comes subsequent?
The most important remaining uncertainty is the transverse velocity of Andromeda. Even small adjustments on this sideways movement could make the distinction between a merger and a close to miss. Future measurements will assist refine this worth and produce us nearer to a clearer reply.
We don’t but have a definitive reply about our personal galaxy’s future. However exploring these potentialities exhibits simply how a lot we’re nonetheless studying concerning the universe – even near house.
