The Milky Way Is Attracting Small Galaxies And Then Snuffing Them Out!

by Madonna Watts D'Souza

The Milky Way Is Attracting Small Galaxies And Then Snuffing Them Out!

January 13, 2021

Who knew the Milky Way is such a spiteful galaxy. Recent data from the Gaia Telescope and Research has revealed that the Milky Way welcomes tinier galaxies towards it, only to strip them of their gases and 'kill' them.

Lights do to incredulous wonders into the stargazing dark skies far away from the city. No one can miss the glorious arm of the Milky Way dashing across the skies. While it may seem that the milky way is all goody-good and an innocent-ethereal swirl of stars, planets and gases in our universe, turns out, it is a surprisingly spiteful interstellar entity!

When did the Milky Way suddenly turn so spiteful, though? Well, the Milky Way was always spiteful; we are only just discovering it. The galaxy is a wolf in sheep’s clothing, indeed. If you were a newborn galaxy floating around in space, dreaming of being one of the most beautiful galaxies ever, the most crucial advice for you would be, “Steer away, far away from the giant Milky Way“.

The good news is that you’re not a galaxy, but the bad news is that you could miss seeing other tiny galaxies floating across in the skies during your stargazing sessions (or dates, if that’s what you’d love to be on)— thanks to the Milky Way.

Antlia 2 (circled) next to the Milky Way (the almost vertical band running down the image)

Tiny Ghost Galaxies in Interstellar Space

We have misunderstood the ghost galaxies floating in the skies. Recent observations from the Gaia Space Telescope have revealed how the Milky Way could overpower the smaller galaxies. So far, around sixty known small galaxies revolve around the Milky Way. Twelve of these galaxies are ‘dim dwarf spheroidals’, and each of these galaxies radiates only a mere 0.0005 to 0.1 per cent of light compared to the Milky Way.

These galaxies have sparsely a few stars sprawled around like a mess, which gives the galaxies a very fragile and ghostly appearance. These galaxies are so hollow and faint that the first one ever found was initially reckoned to be a dirty fingerprint on the photographic plate (talk about a messy ‘plate’).

Here’s where these galaxies were so misunderstood— they were once full of light and twinkled with young ‘baby’ stars. The recent study discovered that when these galaxies initially crossed the Milky Way’s gravitational domain, they lit up to produce even more new stars.

But then, the Milky Way changed its colours, and the tiny galaxies stopped creating stars in most cases and turned dark, hollow and sparse. This is because the Milky Way robbed these remote galaxies from their gas, the components or even the infamously called ‘stardust’ required for star formation.

The Study Caught the Milky Way Red-handed

Masashi Chiba, an astronomer from the Tohoku University in Sendai, Japan, and his then-graduate student Takahiro Miyoshi, observed and analysed seven tiny spheroidal galaxies across the Milky Way. With the help of the European Space Agency’s (ESA) Gaia spacecraft, which had previously measured the galaxies’ movements, the astronomers calculated the galaxies’ orbits around the Milky Way’s centre.

Results showed that these galaxies’ orbits are elliptical, which means that they first get close and then drift away from the Milky Way’s centre. The researchers later compared those orbits to the time when these dwarf galaxies initially created their stars.

According to Chiba, “We found that there’s a very nice coincidence between the timing of the first infall of the satellite [toward the Milky Way] and the peak in the star formation history.” The results were published online at arXiv.org on 23rd October 2020.

The researchers connected the birth of new stars in the dwarf galaxies to the ones in the Milky Way. They discovered that the gigantic Milky Way extracted all of the tiny galaxies’ gases. This caused the remote galaxies to collapse and in turn, gave birth to several budding stars.

However, it was observed that galaxies away from the Milky Way on the opposite end preserved their gases for more extended periods. Only those who dared to drift closer to the Milky Way, especially its centre, were doomed to be wiped out from existence. We may live in the belly of a snake, everyone!

The subject of this NASA/ESA Hubble Space Telescope image is a dwarf galaxy named NGC 5949. Thanks to its proximity to Earth — it sits at a distance of around 44 million light-years from us, placing it within the Milky Way’s cosmic neighbourhood — NGC 5949 is a perfect target for astronomers to study dwarf galaxies. With a mass of about a hundredth that of the Milky Way, NGC 5949 is a relatively bulky example of a dwarf galaxy. Its classification as a dwarf is due to its relatively small number of constituent stars, but the galaxy’s loosely-bound spiral arms also place it in the category of barred spirals.

Past Victims: Draco and Leo

The Draco galaxy was a dwarf galaxy that floated into the Milky Way’s domain around eleven billion years ago. It synthesised many new stars and lost all of its gases to the Milky Way’s annihilatory excursion.

The most recent victim was Leo- the dwarf galaxy, which drifted into the Milky Way territory two billion years ago. Just like Draco, Leo had its excellent star-firework display, only to become an empty vessel floating aimlessly in space. This period was expected to coincide with Leo’s last explosion of new star births.

Chiba added to it and said, “Those two galaxies kept their interstellar gas inside them so that the star formation continued.” However, once depleted, the magic of making new stars for billions of years disappeared, and these galaxies became two souls living in a ghost-town.

Why does the Milky Way do this?

It looks like we’ll need to observe more victims, to find out about it. For now, the Milky Way is quite busy expanding itself, as well as heading towards a spectacular collision with an infamous neighbouring galaxy visible from the Earth- the Andromeda Galaxy.

When will this rare collision happen? In about four billion years, so yes the speed at which the Milky Way is headed towards Andromeda is fast, but we won’t be alive to see it, unfortunately. Until then, all we can do is pack our bags and set out far away from the city, to observe the beautiful Milky Way— the stars and the constellations in the night sky.

But one thing is sure — just like the Moon, our galaxy too has a dark side.

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