Did Andromeda crash into the Milky Way 10 billion years ago?

Jul 04, 2013
A schematic diagram showing how the Andromeda Galaxy (at bottom right) collided with the Milky Way (at the intersection of the axes) 10 billion years ago, moved out to a maximum distance of more than 3 million light years and is now approaching our Galaxy once again. The yellow line shows the track of Andromeda with respect to the Milky Way. Credit: Fabian Lueghausen / University of Bonn

(Phys.org) —For many years scientists have believed that our Galaxy, the Milky Way, is set to crash into its larger neighbour, the Andromeda Galaxy, in about 3 billion years' time and that this will be the first time such a collision has taken place. But now a European team of astronomers led by Hongsheng Zhao of the University of St Andrews propose a very different idea; that the two star systems collided once before, some 10 billion years ago and that our understanding of gravity is fundamentally wrong. Remarkably, this would neatly explain the observed structure of the two galaxies and their satellites, something that has been difficult to account for until now.  Dr Zhao will present the new work at the RAS National Astronomy Meeting in St Andrews on Thursday 4 July.

The Milky Way, made up of about 200 billion stars, is part of a group of galaxies called the Local Group. Astrophysicists often theorise that most of the mass of the Local Group is invisible, made of so-called dark matter. Most believe that across the whole universe, this matter outweighs 'normal' matter by a factor of five. The dark matter in both Andromeda and the Milky Way then makes the between the two galaxies strong enough to overcome the expansion of the cosmos, so that they are now moving towards each other at around 100 km per second, heading for a collision 3 billion years in the future.

But this model is based on the conventional model of gravity devised by Newton and modified by Einstein a century ago, and it struggles to explain some properties of the galaxies we see around us. Dr Zhao and his team argue that at present the only way to successfully predict the total gravitational pull of any galaxy or small , before measuring the motion of stars and gas in it, is to make use of a model first proposed by Prof. Mordehai Milgrom of the Weizmann Institute in Israel in 1983.

This modified (Modified Newtonian Dynamics or MOND) describes how gravity behaves differently on the largest scales, diverging from the predictions made by Newton and Einstein.

Dr Zhao (University of St Andrews) and his colleagues have for the first time used this theory to calculate the motion of Local Group galaxies. Their work suggests that the Milky Way and Andromeda galaxies had a close encounter about 10 billion years ago. If gravity conforms to the conventional model on the largest scales then taking into account the supposed additional pull of dark matter, the two galaxies would have merged.

An image of the Andromeda Galaxy (from top left to bottom right across the centre), made using a filter that selects the light of the hydrogen alpha spectral line. Credit: Adam Evans

"Dark matter would work like honey: in a close encounter, the Milky Way and Andromeda would get stuck together, figuratively speaking", says team member Prof. Pavel Kroupa from Bonn University. "But if Milgrom's theory is right", says his colleague Dr Benoit Famaey (Observatoire Astronomique de Strasbourg), "then there are no dark particles and the two large galaxies could have simply passed each other thereby drawing matter from each other into long thin tidal arms."

New little galaxies would then form in these arms, "a process often observed in the present-day universe", adds team member Fabian Lueghausen, also from Bonn.   Dr Zhao explains: "The only way to explain how the two galaxies could come close to each other without merging is if isn't there. Observational evidence for a past close encounter would then strongly support the Milgromian theory of gravity."

Just such a signature might already have been found. Astronomers struggle to account for the distribution of dwarf galaxies in orbit around both the Milky Way and Andromeda. The dwarf galaxies could be explained if they were born from gas and stars ripped out of the two parent galaxies during their close encounter.

Pavel Kroupa sees this as the 'smoking gun' for the collision. "Given the arrangement and motion of the dwarf , I can't see how any other explanation works", he comments.

The team now plan to model the encounter using Milgromian dynamics and are developing a computer code at Bonn University for this purpose.

In the new model, the Milky Way and Andromeda are still going to crash into each other again in the next few billion years, but it will feel like 'deja vu'. And the team believes that their discovery has profound consequences for our current understanding of the Universe. Pavel Kroupa concludes, "If we are right, the history of the cosmos will have to be rewritten from scratch."

Explore further: Eta Carinae: Our Neighboring Superstars

More information: A preprint of the the paper, entitled "Local Group timing in Milgromian dynamics. A past Milky Way-Andromeda encounter at z>0.8", is available from arxiv.org/abs/1306.6628

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User comments : 34

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dogbert
1.8 / 5 (21) Jul 04, 2013
We keep revisiting MOND because it makes a lot more sense than imaginary matter.
Tuxford
1.6 / 5 (21) Jul 04, 2013
Hear hear.

According to LaViolette, the MOND effect is largely confirmed in his physical model, Subquantum Kinectics. And in SQK, dark matter is simply an optical refraction effect, caused by the nearby presence of mass, which causes the underlying diffusive subquantum medium to approach a critical state needed to initiate new mass to form. Hence, dark matter halos surrounding many galaxies form naturally slowly over time. No need to invent another particle. The missing mass conclusions are based largely on missing imaginations and faulty physical models.

http://phys.org/n...ace.html

http://phys.org/n...fty.html
Requiem
3.7 / 5 (12) Jul 04, 2013
^ Aetherbergers
philw1776
2.3 / 5 (11) Jul 04, 2013
Interesting. But is there additional observational evidence say from the relatively nearby easily observed Virgo cluster which could possibly falsify either MOND or the standard theory of gravity? Lots more possibilities of past galactic encounters there. I would also think that radial velocity measurements of the many "presently" observed galactic collisions could be subjected to statistical analysis that would favor one theory vs another.
Torbjorn_Larsson_OM
3.8 / 5 (23) Jul 04, 2013
"that the two star systems collided once before, some 10 billion years ago and that our understanding of gravity is fundamentally wrong."

Oh, bonkers. I didn't think this was another crackpot theme article, on a general set of idea now rejected by the amazingly successful inflationary standard cosmology. These ideas of 'alternative gravity' are _known_ to be " fundamentally wrong".

Phys.org has been a convenient feed, but I may decide to find a replacement that cares for science.

And as always, there is no astrology, homeopathy, reiki, "design/creation", "aether", "electric/plasma universe" or "MOND". Just stop visiting science sites, and barf your idiocy on your crackpot sites instead.
cantdrive85
1.3 / 5 (25) Jul 04, 2013
The Marcello Truzzi guide the for the characteristics of pseudoskeptics: i.e. bjorn larssen DA
1 Denying, when only doubt has been established
2 Double standards in the application of criticism
3 The tendency to discredit rather than investigate
4 Presenting insufficient evidence or proof
5 Assuming criticism requires no burden of proof
6 Making unsubstantiated counter-claims
7 Counter-claims based on plausibility rather than empirical evidence
8 Suggesting that unconvincing evidence provides grounds for completely dismissing a claim

Check, check, and check! Tbum Lordsen DA is full fledged pseudoskeptic.
dogbert
1.7 / 5 (23) Jul 04, 2013
Torbjorn_Larsson_OM,

Just curious as you seem to know. Why do people prefer to create imaginary mass to normalize our observations of gravity at stellar distances rather than seek to understand why our models fail to match our observations?

I like fantasy but I try to live in the real world.
JohnGee
3.2 / 5 (16) Jul 04, 2013
Dogbert, ever seen an atom?
dogbert
1.4 / 5 (19) Jul 04, 2013
JohnGee,
You've gone very far into fantasy land if you believe atoms are imaginary.
JohnGee
3.1 / 5 (15) Jul 04, 2013
Atoms aren't imaginary, but have you ever seen one? Seems like you should be making the argument that atomic theory is a failed model.

I'm not a moron, so you won't see me doing that.
Requiem
4.1 / 5 (17) Jul 04, 2013
Pseudoskeptic! Hahahaha!

So, if you subscribe to the basic scientific tenet that something must be disprovable before it means anything more than suggesting that the cookie monster dropped trow and pooped out the entire universe, you are now a pseudoskeptic?

Lol. It shouldn't surprise me that you cranks are capable of that level of hypocrisy.
dogbert
1.9 / 5 (21) Jul 04, 2013
JohnGee,
Atoms aren't imaginary, but have you ever seen one?


No, but I am breathing oxygen, nitrogen, carbon dioxide, etc. I have a box of sodium chloride. I have an iron skillet in my kitchen. There is a roll of aluminum foil in my kitchen cabinet.

Do you have any imaginary matter in any form at all? Of course not because it is imaginary.
rwinners
1.8 / 5 (5) Jul 05, 2013
Dr Zhao explains: "The only way to explain how the two galaxies could come close to each other without merging is if dark matter isn't there.:"

10 billion years..... perhaps something has changed.....
rwinners
1 / 5 (2) Jul 05, 2013
The Marcello Truzzi guide the for the characteristics of pseudoskeptics: i.e. bjorn larssen DA
1 Denying, when only doubt has been established
2 Double standards in the application of criticism
3 The tendency to discredit rather than investigate
4 Presenting insufficient evidence or proof
5 Assuming criticism requires no burden of proof
6 Making unsubstantiated counter-claims
7 Counter-claims based on plausibility rather than empirical evidence
8 Suggesting that unconvincing evidence provides grounds for completely dismissing a claim

Check, check, and check! Tbum Lordsen DA is full fledged pseudoskeptic.


A long know practice in politics.....
Neinsense99
4 / 5 (21) Jul 05, 2013
Caution: this galaxy makes wide turns.
rwinners
4.3 / 5 (6) Jul 05, 2013
Caution: this galaxy makes wide turns.

LOL!
nowhere
5 / 5 (5) Jul 05, 2013
dogbert

Why do people prefer to create imaginary mass

How do particles interact?
Are there multiple methods of interaction?
Do all particles use all methods of interaction?
If a particle used only one method of interaction, would it be construed imaginary?
nowhere
5 / 5 (4) Jul 05, 2013
I like fantasy but I try to live in the real world.

The "real world", as defined by a being existing in a separate lesser fraction of the total world, could be said to be the fantasy world.
alfie_null
5 / 5 (6) Jul 05, 2013
And as always, there is no astrology, homeopathy, reiki, "design/creation", "aether", "electric/plasma universe" or "MOND". Just stop visiting science sites, and barf your idiocy on your crackpot sites instead.

Just a small number of them, but unfortunately pretty vocal. Note that many have otherwise been proponents of extreme political views, conspiracy theories, etc. In a science context, makes me wonder how one's brain could become miswired such that one embraces this sort of social interaction.
Neinsense99
3.4 / 5 (13) Jul 05, 2013
And as always, there is no astrology, homeopathy, reiki, "design/creation", "aether", "electric/plasma universe" or "MOND". Just stop visiting science sites, and barf your idiocy on your crackpot sites instead.

Just a small number of them, but unfortunately pretty vocal. Note that many have otherwise been proponents of extreme political views, conspiracy theories, etc. In a science context, makes me wonder how one's brain could become miswired such that one embraces this sort of social interaction.

(Trolls) Mom! They're pickin' on me again!
GSwift7
3.9 / 5 (11) Jul 05, 2013
So, they are basically saying that they 'think' they may have found a real world situation that 'might' fit MOND, but they haven't modeled it yet, so they don't really know if the math works or not, but they issued a press release anyway.

I would have liked to have been there when they did their presentation at the RAS National Astronomy Meeting in St Andrews yesterday. I can just imagine when they get to the part where they say "some 10 billion years ago and that our understanding of gravity is fundamentally wrong" and then there's a mad rush of people trying to get out of the room all at once.

When they say that they are presenting this at the RAS meeting, I wonder if they actually have an invitation to speak, or if they will be standing in the hallway on a chair, shouting at people as they pass and pushing handbills at them.
Neinsense99
3.5 / 5 (13) Jul 05, 2013
So, they are basically saying that they 'think' they may have found a real world situation that 'might' fit MOND, but they haven't modeled it yet, so they don't really know if the math works or not, but they issued a press release anyway.

I would have liked to have been there when they did their presentation at the RAS National Astronomy Meeting in St Andrews yesterday. I can just imagine when they get to the part where they say "some 10 billion years ago and that our understanding of gravity is fundamentally wrong" and then there's a mad rush of people trying to get out of the room all at once.

When they say that they are presenting this at the RAS meeting, I wonder if they actually have an invitation to speak, or if they will be standing in the hallway on a chair, shouting at people as they pass and pushing handbills at them.

If the latter, they could also sell apples and pencils. Just trying to help. :)
tadchem
5 / 5 (3) Jul 05, 2013
I would like to hear the MOND explanation of the high degree of radial symmetry in both of a pair of galaxies *after* a supposed collision. Nearly all the galactic collisions we have documented so far show a high degree of post-collision asymmetry in both participating galaxies.
GSwift7
3.8 / 5 (10) Jul 05, 2013
If the latter, they could also sell apples and pencils. Just trying to help. :)


Then their next press release could read "Experiment which refutes standard theory of gravity receives funding from the RAS"

I would like to hear the MOND explanation of the high degree of radial symmetry in both of a pair of galaxies *after* a supposed collision


You have to take the extra dimensions into account, because the aether waves propogate in the alternate universes such that symetry is maintained on average due to the multi-dimensional birkland currents in the double layers, as demonstrated in cold fusion experiments on the secret government space station at the top of the secret space elevator in China, where they test flying saucer aircraft with visible light cloaking technology and commune with gaia.
Benni
1 / 5 (6) Jul 05, 2013
I would like to hear the MOND explanation of the high degree of radial symmetry in both of a pair of galaxies *after* a supposed collision. Nearly all the galactic collisions we have documented so far show a high degree of post-collision asymmetry in both participating galaxies.


I started wondering exactly the same thing at the instant I looked at the photo of Andromeda, I wondered to myself why it doesn't have the remotest appearance of something already having been in near collision with another galaxy.

I suppose 10 Gyrs can heal a lot of scars, but I would at least expect to see some scar tissue, not just a few nearby gravitationally bound locals.
dogbert
1 / 5 (10) Jul 05, 2013
tadchem,

I would like to hear the MOND explanation of the high degree of radial symmetry in both of a pair of galaxies *after* a supposed collision.


From the article:
Their work suggests that the Milky Way and Andromeda galaxies had a close encounter about 10 billion years ago.


Ten billion years is a long time. Both the Milky Way and Andromeda are supposed to have consumed other, smaller companions during that time. I would think that 10 billion years could smooth out a lot of perturbations.
VendicarE
4.3 / 5 (12) Jul 05, 2013
"And as always, there is no astrology, homeopathy, reiki, "design/creation", "aether", "electric/plasma universe" or "MOND"." - Larsson

Ya but the sun really is a big ball of solid iron and Martini and Rossi's E-Cat is the real deal.
JohnGee
3.4 / 5 (13) Jul 05, 2013
Ya but the sun really is a big ball of solid iron

The fact that libertarian child-molester Omatumr no longer posts gives me hope for this place.
ValeriaT
Jul 06, 2013
This comment has been removed by a moderator.
Fleetfoot
4.5 / 5 (8) Jul 06, 2013
We keep revisiting MOND because it makes a lot more sense than imaginary matter.


MOND is based on Newtonian gravity and that gets the bending of starlight by the Sun wrong by a factor of two. Nobody treats MOND as a valid alternative, it wa sonly ever supposed to be a starting point for other theories. These guys should be looking at TeVeS or STVG if they want to test potential alternatives.

Dr Zhao explains: "The only way to explain how the two galaxies could come close to each other without merging is if dark matter isn't there.:"


TeVeS and STVG are closer to making accurate predictions, but they also require dark matter to account for dense cluster observations.

10 billion years..... perhaps something has changed.....


That's roughly the time when the galaxies were forming out of collisions of smaller proto-galaxies. Are we sure those didn't alter their merged paths slightly?
Fleetfoot
5 / 5 (5) Jul 06, 2013
Ten billion years is a long time. Both the Milky Way and Andromeda are supposed to have consumed other, smaller companions during that time. I would think that 10 billion years could smooth out a lot of perturbations.


Each such merger would alter the momentum of the resulting larger galaxy to be the sum of the momenta of the precursor galaxies. How did they take those velocity vector changes into account in extrapolating the paths backwards over such a long period whenthey don't even know what collisions occurred?
VendicarE
5 / 5 (7) Jul 06, 2013
"libertarian child-molester Omatumr no longer posts" - John

You forget John. According to Libertarians there is no legitimate claim of molestation if the child is willing.
cantdrive85
1 / 5 (14) Jul 06, 2013
"libertarian child-molester Omatumr no longer posts" - John

You forget John. According to Libertarians there is no legitimate claim of molestation if the child is willing.

He would know John, vendiyes never said no to his uncle Billy or his grandpa Joe.
VendicarE
5 / 5 (8) Jul 06, 2013
"He would know John" - CantDriveTooStupid

Yup, I would know since I have read the Libertarian party Platform.

Why haven't you?

Neinsense99
2.5 / 5 (8) Jul 09, 2013
"He would know John" - CantDriveTooStupid

Yup, I would know since I have read the Libertarian party Platform.

Why haven't you?


To be a Libertarian, you have to be a Fibbertarian.

fib

fib
[fib] Show IPA noun, verb, fibbed, fib·bing.
noun
1.
a small or trivial lie; minor falsehood.
verb (used without object)
2.
to tell a fib.