Is The Milky Way a Zombie Galaxy? Some Scientists Say Yes

Friday, 16 March 2018 - 11:06AM
Astrophysics
Solar System
Friday, 16 March 2018 - 11:06AM
Is The Milky Way a Zombie Galaxy? Some Scientists Say Yes
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Image Credit: Pixabay Composite
The Milky Way galaxy might be dead.

It just hasn't stopped moving yet.



Scientists are investigating the theory that our galactic home might fall into the "Green Valley" category, which describes galaxies that have run out of fuel but are still producing new stars.

Green Valley galaxies – believed to be named after a retirement home in Arizona – are galaxies that look entirely healthy, with plenty of new stars being born. In reality, they are cut off from new reserves of cold hydrogen gas, which is the primary source of energy and material for cosmic expansion and growth.

A fundamental law of physics states matter cannot be created or destroyed; as such, galaxies need to get their materials from somewhere. The bulk of this material (especially for new galaxies) comes from halos of dark matter that stretch across the universe. Since we can't in any way perceive or measure dark matter, we don't know exactly what's going on here. One thing, at least, is certain: galaxies take cold hydrogen gas from these dark matter clouds and turn it into stuff we can observe.

Once the hydrogen reserve runs out and a galaxy is cut off from any new material, the galaxy stops producing stars... And dies.

This is difficult to spot because, for collections of giant burning gas balls, galaxies are actually fairly energy efficient. Much of the hydrogen gas used to create a star is eventually recycled: stars collapse into themselves, swirl around in giant clouds, and eventually burst forth into new stars.



Star production can continue in this way long after a galaxy has stopped receiving new fuel from a dark matter halo. Essentially, a Green Valley galaxy is literally running on fumes, recycling its gas reserves over and over so that it appears healthy at first glance.

Evidence suggests that our nearest galaxy, Andromeda, is a zombie, having fallen into the Green Valley category as it burns through its slowly depleting energy reserves. Eventually, the galaxy will run out of cool hydrogen gas and star production will stop entirely.

Similarly, scientists are now investigating the Milky Way itself, looking for evidence that our home galaxy might be quietly waning despite appearing perfectly healthy.

If the Milky Way is secretly a zombie, it won't make much difference to humanity. The galaxy isn't going to suddenly stop spinning, our sun won't instantly blink out of existence, and business will continue as usual for a few more thousand years.

This is simply an uncomfortable reminder that the universe is far bigger and stranger than we like to think. Our little species is a tiny blip in the grand scheme of things – in a billion years of our time, the Milky Way will rotate all the way around only once.

It sure does suck to be so insignificant, huh?
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