How do galaxies die?

How do galaxies die?
Artist’s conception of the Milky Way galaxy. Credit: Nick Risinger

Everything eventually dies, even galaxies. So how does that happen?

Time to come to grips with our galactic mortality. Not as puny flesh beings, or as a speck of rock, or even the relatively unassuming ball of plasma we orbit.

Today we're going to ponder the lifespan of the galaxy we inhabit, the Milky Way. If we look at a galaxy as a collection of stars, some are like our Sun, and others aren't.

The Sun consumes fuel, converting hydrogen into helium through fusion. It's been around for 5 billion years, and will probably last for another 5 before it bloats up as a red giant, sheds its outer layers and compresses down into a white dwarf, cooling down until it's the background temperature of the universe.

So if a galaxy like the Milky Way is just a collection of stars, isn't that it? Doesn't a galaxy die when its last star dies?

But you already know a galaxy is more than just stars. There's also vast clouds of gas and dust. Some of it is primordial hydrogen left from the formation of the universe 13.8 billion years ago.

All stars in the Milky Way formed from this primordial hydrogen. It and other similar sized galaxies produce 7 bouncing every year. Sadly, ours has used up 90% of its hydrogen, and star formation will slow down until it both figuratively, and literally, runs out of gas.

The Milky Way will die after it's used all its star-forming gas, when all of the stars we have, and all those stars yet to be born have died. Stars like our Sun can only last for 10 billion years or so, but the smallest, coolest red dwarfs can last for a few trillion years.

That should be the end, all the gas burned up and every star burned out. And that's how it would be if our Milky Way existed all alone in the cosmos.

Fortunately, we're surrounded by dozens of , which get merged into our Milky Way. Each merger brings in a fresh crop of stars and more hydrogen to stoke the furnaces of star formation.

There are bigger galaxies out there too. Andromeda is bearing down on the Milky Way right now, and will collide with us in the next few billion years.

When that happens, the two will merge. Then there'll be a whole new era of star formation as the unspent gas in both galaxies mix together and are used up.

Eventually, all galaxies gravitationally bound to each other in this vicinity will merge together into a giant elliptical galaxy.

How do galaxies die?
The Andromeda Galaxy. Credit: Adam Evans

We see examples of these fossil galaxies when we look out into the universe. Here's M49, a supermassive . Who knows how many grand spiral galaxies stoked the fires of that gigantic cosmic engine?

Elliptical galaxies are dead galaxies walking. They've used up all their reserves of star forming gas, and all that's left are the longer lasting stars. Eventually, over vast lengths of time, those will wink out one after the other, until the whole thing is the background temperature of the universe.

How do galaxies die?
Eta Carinae shines brightly in X-rays in this image from the Chandra X-Ray Observatory.

As long as have gas for , they'll keep thriving. Once it's gonzo, or a dramatic merger uses all the gas in one big party, they're on their way out.

What could we do to prolong the life of our galaxy? Let's hear some wild speculation in the comments below.

Explore further

What was here before the solar system?

Source: Universe Today
Citation: How do galaxies die? (2015, June 5) retrieved 21 October 2019 from
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Jun 05, 2015
(speculating) I suppose merging with andromeda will be end game for the tier both the MW and andromeda are playing (grand spiral) and start the (possibly) long and grueling transformation to an elliptical and thus our party days are over until that elliptical goes on to consume another unlikely victim. IF we had the power and ability to change the direction of the galaxy (pls remember this is fantasy speculation) it would be a better outcome to RAM the MW into the Triangulum galaxy which has little current evidence of a Central SMBH (or for u other crazies a greycore star or some..i dono insert your own idea ) If the MW could collide with M33 instead of andromeda I speculate the MW would not have much competition for all that gas and stars as compared to a fight with m31's SMBH/central mass/whatever u want to believe. M31's smbh and sgtA* according to simulations will push away most of our gas and just decrease the amount of time we have as a galaxy to LIVE in this STATE

Jun 05, 2015
(continued speculation) whereas merging with a galaxy without a SMBH our sgtrA* could have, essentially, free reign over all the leftover materials in M33. I would think such a collision would allow sgtrA* to gain more and more mass and begin to accrete all the gas around itself making a larger grand spiral or lenticular. We would still have to wrestle with M33's gravity and possibly Dark matter which will distort the MW but not nearly as badly as a battle with a LARGER SMBH ,such as M31 has, would probably leave us or more likely consume us into it. fun fun fun

Jun 05, 2015

Speculation yes, but well thought out and entertaining .

Jun 06, 2015
"Once it's gonzo, ..." ???

Jun 06, 2015
"All stars in the Milky Way formed from this primordial hydrogen. It and other similar sized galaxies produce 7 bouncing baby stars every year."

In fact we can not know whether even only one star in this vast universe is formed in agreement with this hypothesis. There is the clear tendency modern cosmological mythology to try to explain our reality with physical phenomena that can not be observed directly because time scale, distances or their size, and which give wide possibilities for free speculations for profesional mage specualtors.

Jun 06, 2015
The universe will remain partialy unknown. We can not observe directly the real processes in the stars and teir cores. We can not observe directly how elementary particles function because time scales and because our observation directly influence their natural behavior. We can not observe how diffrerent organeles in the living cells are functioning. We can see only single frames of the real time move and to try to deduce the hole move. It this process the probability to make wrong conclusions and offer false hypotheses is too large. We have small posibilities for direct observations and this is main factor that limit our ability to explore the reality at fundamental level. To see the whole picture we should have at least one level higher in the hierarchy.

Jun 06, 2015
The universe will remain partialy unknown. We can not observe directly the real processes in the stars and teir cores.
but that doesnt mean we cant figure out what is happening
case in point:
we cannot directly see what is going on during a fission explosion of hydrogen (as in the hydrogen bomb)
HOWEVER, we can model it, and the subsequent modeling was accurate enough to make very specific predictions which then gave rise to a weapon which ended WWII... that same PHYSICS was utilised to create a secondary power source that was not based upon fossil fuels (nuclear energy) and is currently being used to generate similar data about fusion

again, this is following the scientific principles and methodology
this is also equivalent to forensic evidence and proving something happened without direct observation of the situation (from blood splatter and transfer to footprints and tracking)

Jun 06, 2015
Yes, I say that nature is not fully undestandable. We have physical limitations that we can not ovecome. The rest is unrealistic expectations dictated by the human ego (the desire to be god by itself). We are here on this planet not to became gods but to learn to be people of God will and not dishonor His name as our father.

Jun 06, 2015
I can not undersand your question? I am talking about different levels of understanding of our reality. We known the basic physical laws and use these in our sicence and daily life. But we do not understand the fundamental base of our reality. And we never will do this.

Jun 06, 2015
":So, let me ask about this in a different way: do you regard astronomers, astrophysicists, geologists, (etc) as "profesional mage specualtors"?"

Yes. Many of them are by their choice or unwittingly misled by colleagues or theories that are not evaluated properly. The scientific degree does make the science. The desire to find the truth moves the world forward in positive direction. The desire to conceal the truth stop the development of society in positive direction, return it back on lowest level and is dictated only by ego and vanity which is too pointless in fact.

Jun 06, 2015
Also, how do you, personally, determine whether "theories" are "not evaluated properly"?

By scientific facts which can be repeatedly verified fby various researchers by experiments or observations.
The known physical laws are the basic level of understanding which are found with our limited physical opportunities for observation and experiments.

Jun 07, 2015
Current wide spred theories in scientific communities acceptet by "consensus" have so many contradictions with the facts of observation and experiments, and I am that surprised that you have not noticed this. This contradictions the theorist (philosophers) always try to patch with unobservable and ilusive meta physical phenomena such as black holes, dark matter and energy, extra dimensions, quantum fluctuations, infinitely elastic vacuum of space and others. Theory that is supported with such hypotheses and meta physiscal phenomena no real have no contribution to human knowledge but only to the status and social and emotional comfort of some people who regularly make compromise with their conscience.

Jun 08, 2015
Viko is just super defensive, and assumes every scientist out there (who doesnt have his specified ok) is attacking and trying to dishonor his GOD. Man's accomplishments are trivial in comparison and we could never understand the very baseline fundamentals that we are striving for. Thats the jist i got. Seems super closed in and boring. whats the point in learning about science then. just to help u get closer to your GOD? NOTHING else? no fun... no...i dono.. fun? Your as close as your gonna get walking bro, come on, no amount of science is gonna kill your belief and all that anyways, look how vigorously you and the others in your same boat fight people just doing science because your afraid and admit it your afraid they might kill your GOD... pathetic how can u call urself close to him if ur that afraid? You die hard devout posters need to buck up i don't think most of the science people are trying to kill your GOD just do fun learning. Cheers

Jun 10, 2015
"... that can not be observed directly..."
And what exactly means "observed directly"? You can't collect any observation data by mind-probing it /anything/. So everything is going through your senses, at least. Does it count for "direct"? Do you wear glasses? If you do, does seeing through them counts for "directly" /enough/? For most of the scientific observation you need some tool - a microscope, a telescope, a spectrometer, a particle smasher and so on and so on - is it /all or any of it/ "direct"?... In general - the therm "direct observation" kind of looses ground too quickly to be taken seriously.
What's about wild ideas - just smash some stars with each other /and maybe add some other massive objects you can spare/ until you get something large enough to burn heavier elements /but not enough to collapse it/ and you are good for some more hundreds of millions to billions of years. Then you can start using what's absolutely unusable by any other means by controllable feeding BH

Jun 10, 2015
That way - by feeding all the mass of a galaxy or more to /a/ black hole/s/ you can manage to survive for quite a long time probably trillions of years. And lets' not forget the dark matter - if you can't find some other way to use it better, you can always use it as food for your BHs. :) And if up to that moment the whole universe hadn't collapsed to itself yet, then hopefully this time will be enough for you to learn how to survive on the faint radiation of the black holes themselves /which would add quite long time to your life :)/...

Jun 10, 2015

Are you a RealityCheck sock puppet or just incapable in writing anything that approaches logic?

Jun 10, 2015
:) Well... Actually, what I said about "direct observation" is logically OK. And the term "direct observation" is used in psychology, not physics /except in popular literature maybe/.
But what I did is speculation. And speculation is what this article is about.
Do you really don't see why?
Well... Correct answer of the question "How humanity could survive death of galaxies?", or to be more precise - the end of the lifecycle of last of their stars should be "We shouldn't know." Because all this should happen after billions of years. More as from the beginning of life on Earth, the supposed age of the Solar system and most likely - the age of the Universe /or what we call currently Universe/, according to established theory. So, if at that time, there's something /something!/ descended from humanity /and I don't say "from humans", not even specify if it would be comprised of human individuals, even the less - biologically evolved from them/...

Jun 10, 2015
... just from the point of view of structural evolution... it probably would be more different from current humans as current humans are from archaea. And the cultural difference, and the difference of knowledge and comprehension of what we call "reality" would surely be... well - "unimaginably different" is really the only thing we can say.
But the author of course can't know how different it will be, so instead he says ... well, based on our current knowledge - speculate, make your wild guess - speculate wildly...
And so... somebody tries to start an argument about if something is "directly observed". :) Really? :)
... And no, physicists don't say "direct observation", experimental physicists says "according to the data, collected in *this* /specifies which one/ experiment, and *that* experiment...", and the astronomers say "according to observation /no "direct" here too/ collected from *here* and *there*"...

Jun 11, 2015
.../and theoretical physicists say "according to *that* theory" - not the Divine Truth either, and they don't pretend that as they aren't religious fundamentalists to/, ... and the cosmologists... there's the least "direct" observation...

And if You still don't understand something, please excuse me, it should be my fault, because English is not my native language.

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