The Milky Way Is Much Less Massive Than Previous Thought

schwit1 writes: New research by astronomers suggests that the Milky Way is about half as massive as previously estimated. It was thought to be roughly the same mass as Andromeda, weighing in at approximately 1.26 x 10^12 solar masses (PDF). This new research indicates its mass is around half the mass of Andromeda. "Galaxies in the Local Group are bound together by their collective gravity. As a result, while most galaxies, including those on the outskirts of the Local Group, are moving farther apart due to expansion, the galaxies in the Local Group are moving closer together because of gravity. For the first time, researchers were able to combine the available information about gravity and expansion to complete precise calculations of the masses of both the Milky Way and Andromeda. ... Andromeda had twice as much mass as the Milky Way, and in both galaxies 90 percent of the mass was made up of dark matter."

Comments

Sponsored by Mars Candies:

[i kan reed]

Try the milky way diet plan. You too can lose 1.3 quadrillion solar masses in just one month trying the Milky Way(TM) diet.

Check out these before and after shots: you can't even see the dark matter anymore.

Re:Sponsored by Mars Candies:

[jfdavis668]

What if I like Three Musketeers better?

Re:Sponsored by Mars Candies:

[roman_mir]

It's the inflation in play here, just like in the economy, the units of measurement are being stretched now, so the same mass measured in different units gives a nominally different answer ;)

Re:Sponsored by Mars Candies:

[Anonymous Coward]

10^12 is not a quadrillion.

Re:Sponsored by Mars Candies:

[i kan reed]

I always forget it's zero indexed.

Also, thanks to the reminder, I've decided that "zillion" most likely is equal to "thousand".

Re:Sponsored by Mars Candies:

[smooth wombat]

It's the inflation in play here, just like in the economy, the units of measurement are being stretched now, so the same mass measured in different units gives a nominally different answer

A better example would be the sizing of women's clothes. What is now a size 4 used to be a size 6 a few years ago but because women are getting fatter, the sizes had to change to make people feel good about themselves.*

* Men don't have to worry as much because their sizes are measured in inches.

Re:Sponsored by Mars Candies:

[roman_mir]

* Men don't have to worry as much because their sizes are measured in inches.

- another type of Milky Way?

Re:Sponsored by Mars Candies:

[mythosaz]

* Men don't have to worry as much because their sizes are measured in inches.

Well, sort of.

Although more common in women's apparel, vanity sizing occurs in men's clothing as well. For example, men's pants are traditionally marked with two numbers, "waist" (waist circumference) and "inseam" (distance from the crotch to the hem of the pant). While the nominal inseam is fairly accurate, the nominal size may be smaller than the actual length by more than an inch in U.S. sizes. In 2010, Abram Sauer of Esquire measured several pairs of dress pants with a nominal waist size of 36 at different U.S. retailers and found that actual measurements ranged from 37 to 41 inches.[7] The phenomenon has also been noticed in the United Kingdom, where a 2011 study found misleading labels on more than half of checked items of clothing. In that study, worst offenders understated waist circumferences by 1.5 to 2 inches. London-based market analyst Mintel say that the number of men reporting varying waistlines from store to store doubled between 2005 and 2011.[8]

Men have been lying about a couple of inches in the pants forever too :)

Re:Sponsored by Mars Candies:

[TheCarp]

Well thanks for that. I was actually wondering recently why it was so hard to shop for pants. I have a hard size anyway, as I am built for a much smaller inseam than my waist (or rest of my torso) would seem to indicate. In fact, I would say if you look at my torso vs legs, I have the torso of someone several inches taller than me, and the legs of someone an inch or two shorter.

Looking back, I think this is why my childhood doctor was always suggesting my weight should be unreasonably low based on her height charts. I mean, she was right, I was overweight, but, not nearly by as much as she made it out, once I got into HS sports I found out her "ideal weight" for me based on height was about 10 lbs less than my lean body mass!

In any case, I find this makes pants shopping hard. Often over the years I have had to buy pants that were too long and then have the legs shortened, which is no help for inseam issues at all.

Re:Sponsored by Mars Candies:

[I'm New Around Here]

Well thanks for that. I was actually wondering recently why it was so hard to shop for pants. I have a hard size anyway, as I am built for a much smaller inseam than my waist (or rest of my torso) would seem to indicate. In fact, I would say if you look at my torso vs legs, I have the torso of someone several inches taller than me, and the legs of someone an inch or two shorter.

My stepson was that way as a teenager. His mother had to buy jeans that fit his waist, then have them altered to remove the extra six inches of length from the legs. And that was with buying the shortest inseam available in the waist size.

Re:Sponsored by Mars Candies:

[hairyfeet]

It AIN'T the men, its the stupid as hell clothing industry thinking any guy besides metrosexuals give a rat's ass about that. I don't know how many guys I've talked to the past few years that are ROYALLY PISSED that they can't just go into a store and grab a pair of size whatever and know it'll fit. We don't care if you call it a 37 or an ummagumma just STICK TO IT so we can just walk in and buy a pair of damned pants without having to try shit on like the girls...is that REALLY so much to ask for?

As for TFA? The correct answer is "we don't know shit, it'll probably change, but for now the number pulled out our collective asses is". hell they can't even make the math work without "dark" this and "dark" that which should automatically be replaced with a little stick figure shrugging its shoulders. I think the only thing we can truly say for certain is how things work in this one little teeny tiny itsy bitsy area, anything else? Its just wild guesses with a LOT of question marks in there.

Re:Sponsored by Mars Candies:

[jrumney]

Spot on. I have a pair of 32" jeans that would fall down if I wasn't wearing a belt, and a pair of 36" trousers that I need to squeeze into. I don't need to go into a changing room to see how these look on me, I'd just as happily take them straight from the shelf to the cashier if I could rely on the sizing.

Re:Sponsored by Mars Candies:

[Anonymous Coward]

What if I like something other than the low-quality faeces that Americans call "chocolate"?

USians have shit food, shit drinks, shit art, shit music, shit films, shit cars, shit working environments, shit schedules, ugly women and no culture. It's no wonder you people are so violent and whiny.

Re:Sponsored by Mars Candies:

[Anonymous Coward]

Maybe you and his mother should have been better role models to prevent him from becoming so fat. Whenever I see a fat kid, I know who hasn't been doing their job as a parent.

Re:Sponsored by Mars Candies:

[Anonymous Coward]

Some of us like to look good. That's why we end up with the pretty girls and you end up with the fat ones.

Re:Sponsored by Mars Candies:

[drumlight]

The astronomers probably just missed the blue car speeding away with the rest of it.

Re:Sponsored by Mars Candies:

[Nyder]

What if I like something other than the low-quality faeces that Americans call "chocolate"?

USians have shit food, shit drinks, shit art, shit music, shit films, shit cars, shit working environments, shit schedules, ugly women and no culture. It's no wonder you people are so violent and whiny.

Haters gonna hate.

Re:Tax Something

[i kan reed]

You're right, please support HR-27-1337, placing a 200% tax on politicizing random science discussions.

In Other News...

[cruff]

The Milky Way Galaxy was seen running off while crying about its impending demotion to dwarf galaxy status.

Good news, everyone!

[ArcadeMan]

The Milky Way is much less massive than previously thought

Good news for everyone who's lactose intolerant.

Dark?

[Pro923]

lHow can they possibly tell how much of the matter is "Dark"? I can get the idea of what they're doing - using the relative speeds of each local galaxy to determine the masses contained within each, but how could they possible determine how much mass in each galaxy wouldn't be seen by using light within the bounds of the visible spectrum?

Re:Dark?

[Anonymous Coward]

They measure the rotation curve - the orbital velocity at various distances from the galaxy's centre - and use those points to calculate the mass binding the orbiting stars. That give the total of dark + visible matter. The mass of normal, stellar matter is estimated from the star counts and knowledge of stars in our own galaxy.

Re:Dark?

[Anonymous Coward]

What makes you think we are bound to the visible spectrum? We have plenty of infrared/UV/radio telescopes.

Personally, I haven't ever understood why physicists say that the dark matter has to be something exotic and not simply particles of dust that aren't bound up in stars, but I assume they have discounted this explanation for a good reason.

Re:Dark?

[gurps_npc]

Dust blocks light and turns it into heat, which it radiates. So it shows up on infrared telescopes you mentioned.

Re:Dark?

[gurps_npc]

It's not just the visible spectrum, it's all radiations levels.

Different amounts of mass result in different star types which give up different types of light. non-star objects - dust, planets, etc. block light and radiate out the energy they absorb as heat.

So by looking at any point, we can tell how much mass it has by the amount and type of light it gives off, including the non-visible spectrum, i.e. heat.

There are a few assumptions made, but it makes a lot of sense, mathematically.

None of it would have been possible before we understood the formulas behind fusion.

Re:Dark?

[Jeremy Erwin]

but how could they possible determine how much mass in each galaxy wouldn't be seen by using light within the bounds of the visible spectrum?

Such "dark matter" would show up on Xrays infrared or radio, so that's not a problem. If, however, the "dark matter" does not interact with electromagnetism, but only with gravity and the weak force, (which would be an extremely odd, and frankly, a not very believable aspect of cosmology) things would get a bit tricky.

Re:Dark?

[Anonymous Coward]

How can they possibly tell how much of the matter is "Dark"?

By simple observation

Re:Dark?

[Anonymous Coward]

They estimate the amount of dark matter from the rotational speed of the galaxy. Basically, a rotating body is in equilibrium between the centripetal pseudo-force that wants it to spread out into an infinitely wide disk, and the binding force (gravity in this case) that wants it to be a perfect sphere. When you look at the amount of visible matter and attempt predict its shape from its rotational speed and mass, you realise the galaxy is the wrong shape. There must be an extra force pulling the stars together. That extra gravitational binding energy comes from dark matter.

Because there has to be so much of it, we're sure it's not just ordinary matter, because that amount of matter would've started to collapse under its own gravity, raising its temperature and pressure and causing it to glow. By definition we would be able to see that on some wavelength or another. Whatever's there must be unable to radiate electromagnetic radiation!

Re:Dark?

[DM9290]

If, however, the "dark matter" does not interact with electromagnetism, but only with gravity and the weak force, (which would be an extremely odd, and frankly, a not very believable aspect of cosmology) things would get a bit tricky.

That is EXACTLY what most of the dark matter is suspected to be and that is what makes it tricky.

Re:Dark?

[Anonymous Coward]

Nope, only gravity,

Re:Dark?

[PvtVoid]

lHow can they possibly tell how much of the matter is "Dark"? I can get the idea of what they're doing - using the relative speeds of each local galaxy to determine the masses contained within each, but how could they possible determine how much mass in each galaxy wouldn't be seen by using light within the bounds of the visible spectrum?

You can see the light. So you do this: 1: Measure the mass of the galaxy. 2: Add up all the mass from the stuff you can see. Subtract (2) from (1).

Re:Dark?

[Anonymous Coward]

They've been mapping Dark Matter based on gravitational lensing. "Nothing" doesn't cause gravitational lensing, so we know something is there, and whatever it is, there is almost 10x more of it than what we can see in the entire EM spectrum from radio to gamma.

Re:Dark?

[Anonymous Coward]

Dark matter is possible one of the worst things they could have ever called it.

I guess gravitational anomaly is too Star-Trecky.

Think of dark matter this way. The numbers doesn't add up.
If you pretend that you have a lot of gravity without actually having matter somewhere out there between the real matter then the numbers add up.

Re:Dark?

[Anonymous Coward]

All known stable forms of matter take only four forms: The lightest charged lepton, the electron, the lightest baryon, the proton, the nearly massless neutrinos, and atomic nuclei built from bound states of protons and neutrons. All but the neutrinos interact with matter in well-known ways that we can definitely measure (they are, or contain, electrically charged particles and therefore emit and scatter photons, which are relatively easily picked up). The neutrinos only undergo weak force interactions, but modern detectors can still pick them up. Their known number density and the limits on their mass mean they can't account for the observed gravitational binding of galaxies.

Any normal matter would interact with the light from objects behind it. This is the origin of effects such as the Lyman Forest which reveals the distribution of cold hydrogen in the flight path of distant light... The bottom line is, baryonic matter in the quantities implied simply has nowhere to hide. It's just too easy to detect ten times a galaxy's mass of matter sprinkled among the galaxy's visible part.

Hence the hypothesis of a particle which has mass but no electric charge, color charges or weak hypercharge. It would cast a gravitational shadow but otherwise be virtually undetectable since it does not undergo any interactions we can make individual particle measurements of. Hence the 'dark' in dark matter. One of the few alternatives to a dark particle is a universe suffused with low-mass black holes, but the lack of either microlensing events or gravitational waves emitted by their scattering off each other is difficult to explain. There are a few other places in GR that you can insert hypothetical terms without making it blow up in the face of observations - in fact Einstein's original cosmological constant very effectively explains accelerating expansion. It's also possible that GR isn't the correct theory of geometrodynamics, and the effect of higher-order curvature terms or such is not zero.

GR and QFT are fundamentally incompatible (GR is classical, QFT is quantum), so while there absolutely must be new physics out there, the question is where the new physics lays and what form it takes (and can we ever reach the energy levels to directly investigate it). The belief among physicists is that the correct theory should be the simplest one which fully explains observed phenomenon - Hence why, for example, GR as currently postulated does not involve any higher order curvatures - and the standard cosmological constant / cold dark matter framework does a remarkable job of explaining the evolution of the universe to its present state with remarkably few parameters.

Re:Dark?

[DanielOom]

Now if the amount of normal steller mattter is known and the galaxy has only half the mass estimated earlier, that should make the amount of unexplained 'dark' matter a whole lot smaller....

Re:Dark?

[quixote9]

Very lucid. Thanks for this. One of the things I've wondered is why it's not usually mentioned that "GR [may not be] the correct theory of geometrodynamics." I mean, why dark matter? Why not, "we don't understand gravity yet"? Or, we don't understand all the possible forces of attraction well enough? What about the Casimir Effect, for instance? What happens if that's somehow additive at cosmic scales? What if we've missed something? (Wouldn't be the first time.) It's probably very obvious that I am NOT any kind of physicist.

But you also sort of answered that. It would take a lot more ad hoc assumptions given our current understanding.

Re:Dark?

[geekoid]

"(which would be an extremely odd, and frankly, a not very believable aspect of cosmology"
says someone, every time something new is found.

Re:Dark?

[grantspassalan]

“What if we've missed something?”

The electric force is 10^36 times greater than gravity. Most humans, including physicists cannot really visualize a number with 36 zeros behind it. Because charges can either attract or repel, the electric forces in the universe ALMOST but not quite in some instances cancel each other. It is the ignoring of this tiny imbalance which is not being accounted for in the motion of the galaxies that causes astrophysicists to suggest the existence of dark matter, dark energy and black holes. None of these strictly mathematical constructs have ever been discovered to actually exist.

Re:Dark?

[Anonymous Coward]

Why not, "we don't understand gravity yet"?

This question is being actively researched by several groups at university physics departments, and parts of other gravity research groups. The problem is that even the researchers themselves admit at talks that the alternative gravity theories don't explain observations as well or as comprehensively as dark matter theories do. It is certainly of interest to mainstream physics, but it hasn't made any big breakthroughs yet. And as much the armchair physicists online complain dark matter theories is just an arbitrary fudge factor, the alternative gravity theories frequently end up being too arbitrary, e.g. with arbitrary scales where things just change to make it match observations better.

Re:Dark?

[Anonymous Coward]

“Most humans, including physicists cannot really visualize a number with 36 zeros behind it.

1,000,000,000,000,000,000,000,000,000,000,000,000

Wow, that was hard!

It's about the number of atoms in 11023 tons of mercury.

Re:Dark?

[Anonymous Coward]

What makes you think the Milky Way is in rotational equilibrium?

What makes you think they can even accurately calculate the rotation of the galaxy if they're 50% off on the mass?

Re:Dark?

[penguinoid]

I mean, why dark matter? Why not, "we don't understand gravity yet"?

Because "we don't understand gravity yet" contains no data and makes no predictions (ie, it may well be true but it is unscientific). I think of dark matter as a list detailing exactly where and how much we don't understand gravity or cosmological particle physics. When someone wants to test a new theory of gravity, they will know where to check for discrepancies with GR by looking at where dark matter is; alternately, when someone wants to test a new theory for cosmological particle physics, they can test whether it produces dark matter in the appropriate places.

Re:Dark?

[dryeo]

Always reminds me of the neutrino, first postulated to balance out some equations and found some 30 years later. I'm sure back then on the slashdot of the day you had people doubting that such a small non-interacting particle could exist.

Re:Dark?

[quixote9]

Yes. That makes sense too. (And yes, I am reading with sigs enabled. Some of them are hilarious :mrgreen:)

Re:Dark?

[anarchyboy]

Yes it would mean there is half as much dark matter in the milky way as we previously would have thought but then there's half as much normal matter as well so you get the same ratio. Of course this has no impact on the total dark matter budget of the universe so it doesn't really have any bearing on our understanding of dark matter.

Re:Dark?

[david_thornley]

The Casimir Effect is very short-ranged. It appears to be based on there being room for forming virtual particles or not (some actual physicist please correct me if I'm wrong).

AFAICT, we don't completely understand gravity, but that's not a scientifically useful statement. If somebody has suggestions for changing General Relativity that match current observations, that would be useful. Apparently, it's hard to do that, and nobody's really succeeded.

Dark matter, on the other hand, seems to explain a lot of things well. Fundamentally, it's some sort of matter that doesn't react electromagnetically, and we already know some matter of that description: the neutrino. It isn't much of a stretch of the imagination to think of something like neutrinos, only a lot more massive. (Nobody knows the actual mass of a neutrino, but it's got to be awful small.) It's extremely plausible. The only problem is that it's difficult to make observable predictions from the theory (some researchers are looking for particular possible forms of dark matter), since as a matter of practicality the only way we can directly manipulate or observe things is electromagnetically.

Re:Tax Something

[Anonymous Coward]

A 200% tax on something worthless?

Misweighed

[Culture20]

Astrophysicist kept his foot on the scale again.

Andromeda is a fattie!

[coinreturn]

Nyah, nyah.

It's okay Milky Way...

[Anonymous Coward]

... I'm not 1.26 trillion solar masses either :(

When the Milky Way and Andromeda galaxies collide

[jphamlore]

Does the new estimate for the mass of the Milky Way galaxy change the expected dynamics when the Milky Way and Andromeda galaxies collide in about 4 billion years?

Milky Way Now Fun Sized

[Anonymous Coward]

For your convenience.

Is this surprising? Twice as many stars

[buback]

I've been taught that Andromeda has approx. 2x as many stars as the Milky Way. I learned this years ago, as far as i can remember.

Is it really surprising news that a galaxy with twice as many stars is twice as massive? Were these researchers just fact-checking?

Re:Is this surprising? Twice as many stars

[Bill, Shooter of Bul]

Well, to be fair, most of the mass is *not* in the stars, but the dark matter. It might be a reasonable inference that twice the stars would also mean twice the dark matter, but that might not necissarily be true.

Re:Is this surprising? Twice as many stars

[buback]

So then really what they are confirming is that inference; that matter and dark matter are in a 1/9 ratio, and that if our galaxy has x stars and Andromeda has 2x stars, then Andromeda will also have 2y dark matter mass to our y matter mass.

That seems to be a more interesting finding.

Re:Is this surprising? Twice as many stars

[buback]

*2y dark matter mass to our y dark matter mass*

It would be 18y dark matter to Milky Way y matter.

Yet another step

[necro81]

Starting from the Earth getting kicked out from the center of the universe to the present hypothesis that visible matter is just a tiny fraction of all the stuff in the universe, having the mass of the Milky Way reduced is just another step in what Carl Sagan called The Great Demotions. Hopefully by now humanity is getting used to it.

Start from scratch

[Marrow]

If they can be that wrong about something so fundamental, then how can they possibly claim to understand things or be right now?

I read an article recently about scientists saying the speed of light is not constant. Has their new variable speed of light calculation been plugged into all these other cosmology equations? Maybe this dark matter fudge factor would disappear and we would stop being wrong by the 1/2 the mass of a galaxy.

Re:Start from scratch

[Anonymous Coward]

c is fixed, but the speed of photons in space varies because space is not empty, even "empty" space is not empty, meaning light is traveling through a dynamic medium.

Re:Start from scratch

[Dragonslicer]

If they can be that wrong about something so fundamental, then how can they possibly claim to understand things or be right now?

It's not like they discovered that Andromeda is actually a 20-foot wide disco ball with funhouse mirrors making it look bigger than it really is. When you're talking about a branch of science that typically works in orders of magnitude, a factor of 2 is a pretty minor change.

Re:Start from scratch

[Anonymous Coward]

There is such a thing as degrees of wrong.

Using Newton's equations and constant gravity on a particle-in-a-vaccum to calculate that I'd be in freefall for 1.8 seconds if I were climbing and fell at the end of a 25 foot runout is "wrong" because I'm not a particle, I'm not in a vaccum, gravity isn't position independent, and one really ought to be using GR instead of Newton. But 1.8 seconds is close enough for the purposes of knowing how long until the rope starts to catch me.

Meanwhile you're acting as if knowing that x'' is not exactly equal to g means that you're free to suggest x'' = 2g... No, you're not, because that flies in the face of observation and is therefore stupid. Any proposed correction to a theory must agree with the original theory(ies), in the regime(s) where the original theory(ies) is/are known to be correct. Which is why for weak fields and low speeds, general relativity reduces to Newton's equations and any proposed replacement must do the same.

So no, observing that space might be dispersive at the parts-per-million level for the very highest energy photons detected does not mean you get to go "lolz stupid scientists have they plugged this into da equationz?!??" as if it somehow invalidates those equations. Any correction to or replacement for Relativity or QFT resulting from such an observation would necessarily also have to leave the vast body of observations that empty space is dispersionless at lower energies untouched.

Re:Start from scratch

[geekoid]

"I read an article recently about scientists saying the speed of light is not constant. "
scientist selling a book. Not scientists, and certainly not consensus.

And what do you mean so fundamental?

Re:Start from scratch

[Anonymous Coward]

Cool, so they'll have no problem if we reduce their funding by a factor of 2 either.

Why is the Local Group moving closer?

[Khomar]

The article says that most of the galaxies are moving apart, but the Local Group is moving closer. Why would the local group be different than the other galaxies? Are there other groups of galaxies that are seeing the same effect, or is the Local Group an anomaly?

Re:Why is the Local Group moving closer?

[PvtVoid]

The article says that most of the galaxies are moving apart, but the Local Group is moving closer. Why would the local group be different than the other galaxies? Are there other groups of galaxies that are seeing the same effect, or is the Local Group an anomaly?

The galaxies in the local group are close enough together to be a gravitationally bound system, and are therefore "decoupled" from the expansion. This is true of any cluster of galaxies, and there are many, many examples of such systems in the universe.

It's the same reason your body doesn't get bigger as the universe expands: the binding forces holding it together are stronger than the (tiny) force pulling it apart due to cosmological expansion.

Re:Why is the Local Group moving closer?

[Anonymous Coward]

It's the same reason your body doesn't get bigger as the universe expands: the binding forces holding it together are stronger than the (tiny) force pulling it apart due to cosmological expansion.

Crap, there goes my theory about the expansion of my waistline.

Re:Why is the Local Group moving closer?

[grep -v '.*' *]

your body ... gets bigger as the universe expands

So THAT'S why I'm so fat -- and here I was afraid it was somehow my fault. Sure glad to hear it's not.

Pass me that last piece of pie, would you?

Re:Why is the Local Group moving closer?

[geekoid]

"Pass me that last piece of pie, would you?"

No. Lose some weight.

Re:Why is the Local Group moving closer?

[budgenator]

I'd assume that all galaxy groups are Gravitationally bound, and when looking at the group you're in, the galaxies would appear to be closing, while the other groups would appear to be opening; this is an effect of Hubble's law, everything is moving away from any observer at 67.80±0.77 (km/s)/ Mpc, thus the farther away, the faster it is going away no matter where you are . Even at that, I've seen several Hubble images showing galaxies colliding just like we're about to do with Andromeda.

Re:Why is the Local Group moving closer?

[Anonymous Coward]

We are part of the Local Group. The galaxies of the Local Group are close enough to each other that the pull of gravity towards the common center of mass overcomes the expansion of the universe.

So we are falling towards each other and will eventually form a big elliptical galaxy. That elliptical forms in about 3-7 billion years from now when the Milky Way collides with Andromeda . All the remaining galaxies of the Local Group will collide with that elliptical, with the process finishing between 100 billion to a trillion years from now.

Re:Why is the Local Group moving closer?

[Anonymous Coward]

Until the Great Rip... LOL

Re:When the Milky Way and Andromeda galaxies colli

[Anonymous Coward]

Lookin' forward to meet hot andromeda chicks when I live till then.

Oh no!

[Anonymous Coward]

That means there's less resources out there??

Guys! Cancel the self-replicating 3D printing asteroid colonies! Looks like we'll have to make do on *this* rock!

85% of gravity is caused by Dark Energy and Matter

[Anonymous Coward]

They are still way off.

accurate or precise?

[Anonymous Coward]

researchers were able to combine the available information about gravity and expansion to complete precise calculations of the masses of both the Milky Way and Andromeda

Precision is not useful here. What we need is accuracy, and it sounds like it was the accuracy that was improved, not the precision.

Also, let's take this new data with a grain of salt. The last scientist also claimed their measurements were accurate (though it's likely these new measurements are more accurate than the previous ones).

The sum total mass of previous thought = zero

[uCallHimDrJ0NES]

Therefore, the Milky Way's mass is less than zero. What a difference an "-ly" makes. They should have sent their words to Lolly's.

Re:The sum total mass of previous thought = zero

[I'm New Around Here]

I think I might be the only one to get that.

Meet you at the grocery store.

With this dark matter thing

[azav]

Is it possible that other stars are just hidden behind other stars and that contributes to a large portion of the missing mass?

Re:With this dark matter thing

[Anonymous Coward]

It's possible. The probability that a given star is behind any star is about 10^-15. To get a large portion of the Milky Way stars behind other stars, we're talking about a probability of about 10^-1500000000000.

Re:With this dark matter thing

[painandgreed]

Is it possible that other stars are just hidden behind other stars and that contributes to a large portion of the missing mass?

No. If hidden by dust, we'd see more infrared heat in space as light emitted by stars has to go someplace. If hidden directly behind other solid objects (besides being so astronomically against the odds that things are only hidden from us), it wouldn't account for observations of galaxies rotations speeds that we see along the axis of rotation rather than against the edge. Even for the galaxies we see on edge, if they were all weighted with the mass on the other side of where we are, the rotations speeds, lensing, and other observational data would be different than what we see.

Don't think that dark matter is some quick answer to explain things away. All the obvious choices such as "it's all normal matter behind other normal matter", "it's just non-radiating normal matter", or "the laws of gravity might be different on the galactic scale" have all been suggested, tested, and found not to hold up first. Dark matter is the only real solution left standing at this point and the astronomers and scientists of the world had to be drug to that conclusion, kicking and screaming, over the decades, long before the public started hearing about it.

Re:With this dark matter thing

[I'm New Around Here]

Dark matter is the only real solution left standing at this point and the astronomers and scientists of the world had to be drug to that conclusion, kicking and screaming, over the decades, long before the public started hearing about it.

Maybe if the ones who started talking about it had used a diffrerent term than "dark matter", it would be easier to accept. We hear about quarks, leptons, muons, and things with spin and flavor, etc. I don't understand all that, since I am not a scientist, but I can believe it is serious. Calling it "dark matter" was a dumb move, because it makes it sound as believable as "pixie dust" or "magic beans". At least, they could have used the Japanese words for it like they did with "tsunami".

Re:With this dark matter thing

[david_thornley]

So you're complaining that it was named in the same spirit as black holes, quarks, gluons, and color (as applied to quarks)?

Re:With this dark matter thing

[I'm New Around Here]

Actually, just the opposite. I even mention quarks as one of the 'weird' things that they made up a term for. "Black hole" isn't all that unusual of a term, and is quite easy to make a mental image of. Color goes with flavor and spin, which are simply properties of things, and the terms can be used creatively with little worry.

But calling the stuff that we can't see, but know it must exist because the equations say so, as "dark matter" was just stupid. The name causes more confusion than it should, even in casual forums such as Slashdot. That is because it is so non-intuitive that all the talk of dark matter in the conversations above centers on something that doesn't make sense. Namely, that the scientists just aren't looking in the right place, or the right way, for the ordinary matter that just doesn't have light reflecting off it. That is what 'dark matter' means, right? No? Well, it sounds like that is what it means. So everyone who isn't an astronomer is confused, and the astronomers can't figure out why.

As I said, they couldn't have created a worse situation if they named the mysterious substance 'pixie dust'. It would be just as non-sensical as 'dark matter'.

Re:With this dark matter thing

[Anonymous Coward]

Namely, that the scientists just aren't looking in the right place, or the right way, for the ordinary matter that just doesn't have light reflecting off it. That is what 'dark matter' means, right?

That is what it potentially meant for a while, including when the phrase was coined. Even after that was ruled out, it is a rather descriptive name, at least as much as black hole. People get plenty wrong about both, or will form wrong pictures about both (e.g. too much emphasis on the hole part of black hole), but that has to do with both being topics that are not in every day experience and being repeatedly dumbed down to very superficial levels in popular media. The name is not what fuels arm chair physicists, and changing it wouldn't have helped. It is at least more descriptive than a penguin diagram.

Color goes with flavor and spin, which are simply properties of things, and the terms can be used creatively with little worry.

They can be used creatively, doesn't mean they get used right either, especially spin which people will screw up all the time.

New name

[gmuslera]

Marketing suggested that now it should be called the Skim Milky Way.

Re:New name

[Anonymous Coward]

"Marketing suggested that now it should be called the Skim Milky Way."

It's not that smaller, it's more like Half Fat Milky Way.

Re:Tax Something

[Shakrai]

You're right, please support HR-27-1337, placing a 200% tax on politicizing random science discussions.

I'd like to support your tax but I fear that the climate change discussions will see a massively improved signal to noise ratio with corresponding decrease in the eye rolling ratio.

What about the supermassive black hole?

[dicobalt]

Did they add the mass of the supermassive black hole at the center of the galaxy?

Re:What about the supermassive black hole?

[wierd_w]

I am more interested in radical ideas, like anti-mass, being at work.

Say you have a large aggregation of mass that is orbiting a large, semistationary singularity-- like, a galaxy does.

Outside this rather bumpy gravity well, you have a diffuse cloud of antimass, which then pushes on, and chases the mass as it rotates around the central mass. This pushing cancels out the centripetal force.

It's an interesting idea, as it was recently postulated that there is no real compelling reason for antimass to not exist-- it is a perfectly valid solution in some circumtances-- meaning that the stuff may very well exist.

It would be interesting to see a reinterpretation of the data of for "dark matter maps" of the universe, with antimass pressure substituted for mystery gravity application-- even if the math doesnt add up.

Re:What about the supermassive black hole?

[tomhath]

Yes, but it turns out to be only a Mediocre Massive black hole

Re:What about the supermassive black hole?

[Anonymous Coward]

This is a gravitational study so every form of mass is already accounted for. The supermassive black hole is only 4 x 10^6 solar masses anyway. It's like worrying about the impact of a flea on the weight of an elephant.

Re:What about the supermassive black hole?

[geekoid]

Since E=mc2, have a negative mass would mean negative energy.

How do you have negative energy content?

Re:What about the supermassive black hole?

[Anonymous Coward]

The correct equation is E^2=m^2*c^4. The popular version assumes no negative mass when taking the square root on both sides.

I am not sure that was what the article said

[Marrow]

http://www.sott.net/article/28...

I'm not sure that this is the same article, but it points out new measurements that may force us to alter the speed at very long distances to deal with quantum effects. (attenuation?)

http://beta.slashdot.org/story...

Re:I am not sure that was what the article said

[Anonymous Coward]

Maybe look at some the slashdot comments on that story (instead of rewriting thing here...), that theory is a curiosity at this point and even the paper it is proposed in says it is unphysical. The author thinks they can come up with a more complete version that isn't unphysical, but that is still to be seen. Even then, it is a an extremely small correction compared to the order of magnitude issues that dark matter theories are trying to address.

This one is closer

[Marrow]

http://www.abovetopsecret.com/...

Does Dark Matter really exist?

[Martin S.]

While it has been widely accepted in recent years that Dark Matter fixes the standard model. Increasing problems suggest that Dark Matter might not actually exist.

Re:Does Dark Matter really exist?

[Anonymous Coward]

I read that article. There's nothing new there. It says that this physicist believes that Einstein's equations are wrong or that our understanding of gravity is flawed. Since the moment we first measured the rotational speeds of nearby galaxies, plugged the numbers into general relativity and noticed a vast difference between the expected result and the observed result, the possibility that Einstein's theory is as flawed as Newton's has been on the table. Unfortunately, no one's come up with anything better. String theory was hoped to do the job but it's incomplete and, so far, completely untestable. The study of theoretical physics, these days, is all about improving on Einstein.

There are only two possibilities. Either most of the mass in the universe is completely invisible and unable to be interacted with or Einstein's formula is merely a good approximation on the nature of gravity at really large distances but falls apart when you start dealing with the huge distances and/or masses at the galactic scale. While it seems more likely that Einstein is flawed his formulas work so very well for everything else and, in fact, work just fine when you treat dark matter as particles with mass but none of the other characteristics of matter.

This article doesn't provide any actual insight into what dark matter is. The physicist seems to think that our concept of gravity is wrong, which is possible, but if your going to make a claim like that you should at least have something else that does the job in the works.

Literally everything about humanity

[Anonymous Coward]

is much less than expected. You guys act like you are hot shit and you can't even leave your own gravity well as a species. You don't even have a base on your nearest astral body. Hell, you still fight over imaginary things like which religion is better. Humanity, get over yourself, you aren't that great.

Re:Literally everything about humanity

[Anonymous Coward]

Hey man, we have a condition! It's genetic!

Shouldn't That Be

[Anonymous Coward]

The Milky Way Is Thought To Be Much Less Massive Than Previous Thought

Gravity? How about magnetic fields?...

[__aanbvm4272]

Helioshperes as well as our own Ionosphere (magnetic field) have shown that magnetism is a universal force to be reckoned with. Indeed gravity could be just a magnetic effect on an atomic scale. The more mass the more effect. Electrons pulsing in a atom synchronizing with identical atoms become a united energy. That's what holds things together. And what gravity is, basically. A united atomic force. Too simple? .

Kevin Sorbo will be pissed...

[Lumpy]

The commonwealth is a lot smaller than expected!

Yes, I went there.... Deal with my vast knowledge of really bad SciFi!

Re:Kevin Sorbo will be pissed...

[geekoid]

OTOH, Quark's garbage route will be shorter.

I saw your bad SCI-F, and raised you :)

Re:Tax Something

[Anonymous Coward]

You can always count on some humorless asshole to downmod. His mother must have forgotten his Lucky Charms during the last grocery run.

Re:Tax Something

[I'm New Around Here]

You can always count on some humorless asshole to downmod. His mother must have forgotten his Lucky Charms during the last grocery run.

Worse. His asshole father ate all the marshmallows in one bowlfull.

Re:Tax Something

[Anonymous Coward]

Funny how they keep going back on forth on the mass of the galaxy. Previously, the Milky Way was thought to be about half as massive as Andromeda, then they say it's the same and now they are going back to saying it's half.

Re:Gravity? How about magnetic fields?...

[Anonymous Coward]

If a magnetic field was holding Jupiter in orbit or holding you to the ground it would be very detectable.

The mass of the galaxy seems fundamental

[Marrow]

But maybe its harder to measure MilkyWay than to measure the mass of other galaxies. Still, they cannot directly measure the mass of anything out there. So they are implying the mass by looking at the light coming from them and from neighboring objects. I would rather look forward to them being proven wrong about their assumptions because we would learn more. Maybe they might learn something that could help us out here on Earth.

So I prefer to look at theories which challenge the accepted science in the hopes that new discoveries might spark new technologies here at home.

Re:The mass of the galaxy seems fundamental

[david_thornley]

We can look at a whole bunch of galaxies from a distance, and see the whole galaxy (except for the dark matter) somehow or another. There's precisely one galaxy that we can see from the inside, and we don't have a good global view of it. It's easier to categorize things we can observe in a similar way.

Hairyfeet's Dunning-Kruger Excursion

[Anonymous Coward]

hell they can't even make the math work without "dark" this and "dark" that which should automatically be replaced with a little stick figure shrugging its shoulders. I think the only thing we can truly say for certain is how things work in this one little teeny tiny itsy bitsy area, anything else? Its just wild guesses with a LOT of question marks in there.

You're never one to let an absence of information keep you from posting, but your knowledge of astronomy and astrophysics is particularly lacking. Just because it's too hard for you to understand does not mean it is incomprehensible to others. Even if what you said were true, you don't know enough to make that judgment. There may be question marks, but you don't even know what they are, let alone any of the answers.

With regard to your willful ignorance of dark matter and energy, consider that neutrinos only interact via the weak force and gravity. Trillions of them pass through you every second, and they go straight on through the Earth as if it weren't there. Now imagine a similar particle that doesn't interact via the weak force. There are at least three separate kinds of observation which suggest such particles exist: galactic rotation curves, certain observations of gravitational lensing, and fluctuations in the CMBR. The only remotely credible alternative theory was that gravity behaves differently on large scales. In order for that to be true, you end up fudging numbers for every single galaxy, and it still doesn't explain the lensing or large-scale structure formation. The Bullet Cluster specifically is generally considered to be direct observational evidence for the existence of dark matter. Note also that the chief critic of that interpretation chose not to publish his interpretation in a scientific journal -- even the supporters of the alternative theory admit that they can't explain the observation.

Now, you can continue to argue from your own personal ignorance that Dark Matter isn't a thing, but since that is fallacious, irrational, and a waste of time on everyone's part, maybe next time you can restrain yourself, aight?

Re:Gravity? How about magnetic fields?...

[david_thornley]

Okay, you've strung words together in an evocative way. (Honestly, I don't know of any way electrons "pulse", or any way atoms synchronize with identical atoms - not to mention that atoms with different numbers of neutrons behave very similarly in many way.) If you can make some sort of mathematical model or theoretical framework that agrees reasonably well with current observations, we can start considering it.

In the meantime, remember that we have ways of detecting magnetic fields, and they aren't strong enough to do what gravity does. Gravity is incredibly weak on an atomic scale, and electromagnetism is incredibly weak on a cosmic scale (since positive and negative charges cancel out, and so basically almost everything on a big scale is electrically neutral).