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THE Milky Way may have already commenced its ill-fated collision with a neighboring galaxy - and scientists predict this could fling the Solar System into deep space.
Our galaxy is classified as a barred spiral, with ribbons of stars, gas, and dust that cut across its heart.
All galaxies are surrounded by a thin veil of gas known as the circumgalactic medium that fills the gaps between them.
While examining this ubiquitous structure, scientists uncovered evidence that the Milky Way has already started its crash-course with Andromeda.
Astronomers from Australia and the United States used the Keck Cosmic Web Imager to capture snapshots of IRAS08, a small spiral galaxy around 270 million light years away.
They peered 90,000 light years beyond the edge of the galaxy to analyze changes in the circumgalactic medium. Their findings were published today in .
Some images featured a stripe of neutral hydrogen gas that linked IRAS08 to a smaller neighboring galaxy, but this is nothing out of the ordinary.
The universe is strung together through a vast network of gaseous filaments and threads of dark matter, forming what is known as the cosmic web.
However, what was unexpected was the discovery of hydrogen that had been stripped of its electrons as it mingled with oxygen.
Atoms have two sources of heating in space: the starlight of distant galaxies and run-ins with other particles.
Scientists can use these metrics to calculate a pattern of ionization expected from a mix of hydrogen and oxygen.
The researchers mapped changes in the density of ionization over a few thousand light years and discovered that starlight from IRAS08 was losing influence.
"In the CGM, the gas is being heated by something other than typical conditions inside galaxies, this likely includes heating from the diffuse emissions from the collective galaxies in the Universe and possibly some contribution is due to shocks," lead author Nikole Nielsen explained.
"It's this interesting change that is important and provides some answers to the question of where a galaxy ends."
In short: galaxies may be bigger than astronomers thought.
These findings can extend more generally to the Milky Way, implying its stars may already be mingling with Andromeda's luminous halo.
Andromeda is another barred spiral located roughly 2.5 million light years away, making it our closest neighbor.
The new findings gave way to two theories. Firstly, it's possible the Milky Way's limits are vaster than we anticipated.
But a second, more sinister theory suggests the much-anticipated collision with Andromeda has already begun.
When galaxies collide, their gravitational fields interact, shifting the alignment of their stars and distorting their appearances.
Andromeda and the Milky Way are expected to merge into a huge elliptical galaxy dubbed "Milkdromeda," though the jury is still out on how this will impact our Solar System.
Calculations from 2007 - note, nearly a decade ago - found a 50% chance that the Solar System would be pushed three times farther from the galactic core than its current distance.
Other researchers have predicted around a 12% chance that the Solar System will be flung into deep space.
Nasa says the Earth and other planets will likely survive, although they may take on new coordinates.
At that point it won't matter, as Earth will no longer have the capacity to sustain terrestrial life.
By the time the galaxies collide in earnest, our planet's surface will be far too hot to support liquid water.
The Sun's brightness increases by roughly 10% every billion years due to the hydrogen burning at its core.
At some point in the distant future, Earth's surface water is expected to evaporate entirely.
Nevertheless, the planet will still be caught in the middle of this intergalactic merger.
If you were to witness it from the ground, Andromeda would grow bigger and bigger in the night sky until it stretched across the horizon like a hazy rainbow.
The good news? If it isn't obvious, we won't be around to see it. The collision is expected to occur around 4.5 billion years in the future.
Nevertheless, the latest evidence contributes to painting a clearer picture of the universe, helping us make sense of the mysteries within.
The Milky Way is the galaxy that contains our Solar System. It is a barred spiral galaxy, meaning it has a central bar-shaped structure composed of stars, and spiral arms that extend outward.
Here are some key features:
Our galaxy is about 100,000 light-years in diameter and contains between 100 billion and 400 billion stars. The Sun is located roughly 27,000 light-years from the galactic center, in one of the spiral arms known as the Orion Arm or Orion Spur.
The Milky Way rotates, with stars in the disk orbiting the galactic center. The speed of rotation varies with distance from the center.
The Milky Way is part of a group of galaxies known as the Local Group, which also includes the Andromeda Galaxy, the Triangulum Galaxy, and about 54 other smaller galaxies.
From Earth, the Milky Way appears as a milky band of light stretching across the sky, which is the combined light of billions of distant stars that are too faint to be seen individually.
