Large, Strangely Dim Galaxy Found Lurking On Far Side of Milky Way

A reader shares a report from Science Magazine: Circling our galaxy is a stealthy giant. Astronomers have discovered a dwarf galaxy, called Antlia 2, that is one-third the size of the Milky Way itself. As big as the Large Magellanic Cloud, the galaxy's largest companion, Antlia 2 eluded detection until now because it is 10,000 times fainter. Such a strange beast challenges models of galaxy formation and dark matter, the unseen stuff that helps pull galaxies together. The galaxy was discovered with data from the European Space Agency's Gaia satellite, a space telescope measuring the motions and properties of more than 1 billion stars in and around the Milky Way. Gabriel Torrealba, an astronomy postdoc at the Academia Sinica in Taipei, decided to sift the data for RR Lyrae stars. These old stars, often found in dwarf galaxies, shine with a throbbing blue light that pulses at a rate signaling their inherent brightness, allowing researchers to pin down their distance.

Gaia data helped the team see past the foreground stars. Objects in the Milky Way's disk are close enough for Gaia to measure their parallax: a shift in their apparent position as Earth moves around the sun. More distant stars appear fixed in one spot. After removing the parallax-bearing stars, the researchers homed in on more than 100 red giant stars moving together in the constellation Antlia, they report in a paper posted to the preprint server arXiv this week. The giants mark out a sprawling companion galaxy 100 times less massive than anything of similar size, with far fewer stars.

Re:

[lgw]

You joke, but a galaxy mostly covered by Dyson swarms would look something like this. It's the hardest problem in the Fermi paradox: Dyson swarms seem inevitable for a high-tech species, and would be visible in other galaxies if there were a lot of them. But we don't see that.

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[should_be_linear]

SIG: "Socialism: a lie told by totalitarians and believed by fools". So, I guess all those Dyson spheres are rented by some intergalactic real estate agency, according to you?

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[lgw]

Not sure what connection you're making. The only central authority needed for a Dyson swarm is traffic control (which is a big deal). The swarm itself is a zillion large objects orbiting the Sun, each of which can be doing its own thing - no need to assume any specific economic system, or even any uniformity of such. None, some, or all could be rented: aliens, who knows?

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[Gavagai80]

Ever more destructive extreme power consumption and environmental destruction is probably not a habit that leads a species to surviving long. Any species advanced enough to contemplate a dyson sphere could not have gotten to that point by being the kind of species that would build one.

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[lgw]

The problem with all such objections is "what, every alien?" All it takes is one faction from one alien species and the galaxy would be covered with Dyson swarms. Presumably alien psychology is no less diverse than humans.

Also, the technology needed to build a Dyson swarm isn't far ahead of what we have now. It's really the scale that makes it impressive, but it's all pretty straightforward. You really only need fusion power, and not even that to get started. We could put a hole in an asteroid and make

But how do we know...

[SqueakyMouse]

Astronomers have discovered a dwarf galaxy

How do we know it's populated by dwarves?

Re:But how do we know...

[Freischutz]

Astronomers have discovered a dwarf galaxy

How do we know it's populated by dwarves?

Dwarves? Don't be silly man! ... with it being so 'strangely dim' and 'luking', this is clearly the home galaxy of THE SITH!!!

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[Sunastar]

To me 'strangely dim' and 'lurking' sounds more like politicians.

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[aliquis]

Strangely dumb and leaving black holes?

Re:But how do we know...

[jfdavis668]

I'm waiting until the find the elf galaxy.

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[account_deleted]

Comment removed based on user account deletion

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[aliquis]

Considering how close they are to earthlings ..

It needs a better name

[GrumpySteen]

It's large and strangely dim. We should call it "Congress."

Re:Strike one problem of our physics list:

[Sique]

Actually no. Dark Matter is not simply "missing matter" in general, it's missing matter in very well defined scenarios. A dark galaxy out there would not solve other problems which are connected to Dark Matter. It wouldn't explain the rotation of galaxies [wikipedia.org] we actually see. It wouldn't explain the behavior of the gas clouds at NGC 604 [wikipedia.org]. It wouldn't explain the amount of light deflection we see at galaxies which bend the light of the galaxies behind them and cause us to see Einstein rings [wikipedia.org].

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[Anonymous Coward]

Besides, wouldn't a really dim galaxy kind of 'be' dark matter since we could not see it before?

If by "dim" you mean the galaxy is far far away, or has lots of dust or small stars, then no, most physicists would not say it is dark matter. Most physicists use the phrase "dark matter" to refer to a non-baryonic mass-producing phenomenon, not protons and neutrons that are poorly illuminated.

Re:But it's a start

[Sique]

Currently, Dark Matter is the term for stuff that causes gravitational effects, but does not interact with electromagnetic fields. Ordinary matter does interact with electromagnetic fields and is often referred to as baryonic matter, but "Hubble pictures are too crisp." We can see light in pictures taken by the Hubble space telescope which has traveled more than 12 billion light years (or is more than 12 billion years old). We don't see any effects of that light to have interacted with baryonic matter during that time (e.g. slight phase differences between different frequencies, degrading sharpness or similar). Thus we can calculate an upper limit of the average amount of ordinary matter in the interstellar space. We can't account for all that baryonic matter yet, but the unaccounted for amount is shrinking, and dark galaxies like the one in the article will make the account more complete. There were other breakthroughs [arxiv.org] recently, but still, this is all baryonic (and thus ordinary and not Dark) matter.

No, Dark Matter is not simply dark matter, matter we haven't seen yet. Dark Matter is matter we absolutely can not see, e.g. detect by its direct interactions with electromagnetic waves. We only can tell that there is Dark Matter out there because it changes Spacetime according to General Relativity. There are models where Dark Matter does interact with the Weak Force (e.g. WIMPs, Weakly Interacting Massive Particles), but so far, none of those models has been proven by an experiment or an observation.

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[Sique]

Exactly. Any problem with that?

Of course there are problems with that. And thus, there are many ideas floating around to come to the same results without Dark Matter. For instance, MOND (MOdified Newtonian Dynamics) is the most famous of them. TeVeS (Tensor–vector–scalar_gravity) is a relativistic generalization of MOND, Gauge vector–tensor gravity another one. The last one is very successful with one exception: It can't explain the diffusion damping necessary to have such an uniform cos

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[painandgreed]

If it plugs the hole for one feature of the universe that is explained currently by dark matter, that is progress. We may find other things that plug the rest of the holes and then there would be no need for dark matter. Besides, wouldn't a really dim galaxy kind of 'be' dark matter since we could not see it before?

Doesn't work that way. Currently we have many holes that all lead to the same conclusion. If one got plugged but didn't plug the others also, it most likely a sign that that solution is wrong, and if it was correct, it would indicate that much weirder things than some matter than doesn't interact with the EM radiation was going on, which seems to be what most dark matter detractors are upset about. Dim galaxies are out also. Dim ordinary matter was one of the first things proposed to plug one of the holes,

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[Anonymous Coward]

"One fainter" is a universally accepted unit of measure, equal to the brightness of a bees-wax candle placed approximately 9 and three-sixty-fourths Furlongs down the end of a dark hallway behind a frosted partition.

Everybody knows that.

So having a dwarf galaxy with a brightness level of 10,000 fainters is obvious not as bright a galaxy such as ours which contains roughly 97 or so fainters, depending on the eyesight of the horse.

This isn't taught in school anymore?

Oh boy! Now with "fluffier dark matter".

[Rambo Tribble]

But will it still have that satisfying crunch?

Rich with heavy elements but dim?

[The Snazster]

So, with the abundance of metallicity and no central uninhabitable core or giant black hole, sentient life developed early there and now they've covered most of the good real estate over with Dyson spheres?