A new study reveals that the collision between the galaxy containing Earth and its giant neighbor may have already begun.
Scientists have long predicted that the Milky Way galaxy, which Earth belongs to, will collide with its “monster” neighbor, Andromeda, in the next 4 to 5 billion years.
However, a recent study published in the journal Nature Astronomy demonstrates that this collision has actually started, although not in the way we previously thought.
The “monster” galaxy Andromeda positioned next to the Milky Way as viewed from Earth – (Graphic: NASA).
According to Science Alert, the new work by Australian and American scientists focused on the galactic halo, also known as the circumgalactic medium (CGM).
This is a vast but dim cloud of material that surrounds the bright disk, which was previously thought to be the entirety of the galaxy.
The galactic halo can account for up to 70% of a galaxy’s mass.
Despite its dominant presence throughout the universe, little is known about the typical structure of this medium, including where it actually ends, making it difficult to distinguish the real boundaries between galaxies.
In the new study, the research team used a highly sensitive instrument to capture images focusing on the relatively small spiral galaxy IRAS 08339+6517 (shortened to IRAS08), located 270 million light-years away.
By capturing a much larger region of space, about 90,000 light-years from the edge of the galaxy’s bright disk, the team was able to analyze characteristic changes in the composition of this medium.
Some images revealed strands of neutral hydrogen connecting IRAS08 with a smaller neighboring galaxy.
However, surrounding these gas strands were ionized hydrogen floating, mixed with oxygen, which only appears when there is a heat source involved.
“We found them everywhere, which is really interesting and somewhat surprising,” said lead author Nikole Nielsen from Swinburne University (Australia).
According to her, the heat source involved in this phenomenon could be shocks—the interaction between IRAS08 and the nearby smaller galaxy, causing atoms to collide.
This means that the invisible halos of these two galaxies have indeed come into contact, even though their bright disks are still far apart.
Applying a similar model to the Milky Way and Andromeda, scientists believe that the halos of both galaxies partially overlap.
This indicates that the collision has begun. But there is no need to worry too much.
Some previous studies have warned that the collision between the Milky Way, a “monster” galaxy in the galactic world, and an even larger adversary like Andromeda, could have catastrophic consequences.
One of these consequences is that Earth could be ejected from the habitable zone of the Solar System.
However, this scenario would only occur when the two main disks of the two “monsters” actually collide in 4 to 5 billion years.
Since the halos of the Milky Way and Andromeda are vast, even if this invisible structure has begun to collide, their star-filled and planetary disks are still about 2.5 million light-years apart.
