Artist's Conception of our Milky Way Galaxy: Blue, green dots indicate distance measurements. CREDIT: Robert Hurt, IPAC; Mark Reid, CfA, NRAO/AUI/NSF

Triple Whammy: Milky Way More Massive, Spinning Faster and More Likely to Collide

Article Updated: 24 Dec , 2015

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For many of us, looking closely in the mirror and stepping on the bathroom scale just after the holidays can reveal a substantial surprise. Likewise, astronomers looking closely at the Milky Way have found our galaxy is more massive than previously thought. High-precision measurements of the Milky Way disclose our galaxy is rotating about 100,000 miles per hour faster than previously understood. That increase in speed, said Mark Reid of the Harvard-Smithsonian Center for Astrophysics, increases the Milky Way’s mass by 50 percent. The larger mass, in turn, means a greater gravitational pull that increases the likelihood of collisions with the Andromeda galaxy or smaller nearby galaxies. So even though we’re faster, we’re also heavier and more likely to be annihilated. Bummer!

The scientists are using the National Science Foundation’s Very Long Baseline Array (VLBA) radio telescope to remake the map of the Milky Way. Taking advantage of the VLBA’s unparalleled ability to make extremely detailed images, the team is conducting a long-term program to measure distances and motions in our Galaxy. At the American Astronomical Society’s meeting in Long Beach, California, Reid said they are using trigonometric parallax to make the measurements. “This is exactly what surveyors use on Earth to measure distances,” he said. “And this is gold standard of measurement in astronomy.”

Trigonometric parallax was first used in 1838 to measure the first stellar distance. However, with better technology, the accuracy is now about 10,000 times greater.

Our solar system is about 28,000 light-years from the Milky Way’s center. At that distance, the new observations indicate, we’re moving at about 600,000 miles per hour in our Galactic orbit, up from the previous estimate of 500,000 miles per hour.

The scientists observed 19 regions of prolific star formation across the Galaxy. In areas within these regions, gas molecules are strengthening naturally-occurring radio emission in the same way that lasers strengthen light beams. These areas, called cosmic masers, serve as bright landmarks for the sharp radio vision of the VLBA. By observing these regions repeatedly at times when the Earth is at opposite sides of its orbit around the Sun, the astronomers can measure the slight apparent shift of the object’s position against the background of more distant objects.

The astronomers found that their direct distance measurements differed from earlier, indirect measurements, sometimes by as much as a factor of two. The star-forming regions harboring the cosmic masers “define the spiral arms of the Galaxy,” Reid explained. Measuring the distances to these regions thus provides a yardstick for mapping the Galaxy’s spiral structure.

The star forming regions are shown in the green and blue dots on the image above. Our sun (and us!) are where the red circle is located.

The VLBA can fix positions in the sky so accurately that the actual motion of the objects can be detected as they orbit the Milky Way’s center. Adding in measurements of motion along the line of sight, determined from shifts in the frequency of the masers’ radio emission, the astronomers are able to determine the full 3-dimensional motions of the star-forming regions. Using this information, Reid reported that “most star-forming regions do not follow a circular path as they orbit the Galaxy; instead we find them moving more slowly than other regions and on elliptical, not circular, orbits.”

The researchers attribute this to what they call spiral density-wave shocks, which can take gas in a circular orbit, compress it to form stars, and cause it to go into a new, elliptical orbit. This, they explained, helps to reinforce the spiral structure.

Reid and his colleagues found other surprises, too. Measuring the distances to multiple regions in a single spiral arm allowed them to calculate the angle of the arm. “These measurements,” Reid said, “indicate that our Galaxy probably has four, not two, spiral arms of gas and dust that are forming stars.” Recent surveys by NASA’s Spitzer Space Telescope suggest that older stars reside mostly in two spiral arms, raising a question of why the older stars don’t appear in all the arms. Answering that question, the astronomers say, will require more measurements and a deeper understanding of how the Galaxy works.

So, now that we know we’re more massive, how do we compare with other galaxies in our neighborhood? “In our local group of galaxies, Andromeda was thought to be the dominant big sister,” said Reid at the conference, “but we’re basically equal in size and mass. We’re not identical twins, but more like fraternal twins. And its likely the two galaxies will collide sooner than we thought, but it depends on a measurement of the sideways motion, which hasn’t been done yet.”

The VLBA is a system of 10 radio-telescope antennas stretching from Hawaii to New England and the Caribbean. It has the best resolving power, of any astronomical tool in the world. The VLBA can routinely produce images hundreds of times more detailed than those produced by the Hubble Space Telescope. The VLBA’s tremendous resolving power, equal to being able to read a newspaper in Los Angeles from the distance of New York, is what permits the astronomers to make precise distance determinations.

Source: AAS, Harvard-Smithsonian Center for Astrophysics


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Venkatesh.S
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Venkatesh.S
January 5, 2009 5:42 PM

This is a interesting question that I came across in a discussion regarding this.

Since extra gravitational force has been detected, does that mean, that dark matter and dark energy will be nullified?

Salacious B. Crumb
Guest
Salacious B. Crumb
January 5, 2009 7:32 PM
I don’t quite believe it, as it smacks of the geocentric view – actually reading IMO more like Americacentric – of the place in the Universe. (Is this science or the American Astronomical Society a self love-fest.) Really, one set of measures doesn’t necessarily make it so, and like most of science, it needs to be independently confirmed. Merely nineteen measures of several regions of the Milky Way might also mean that there might be other localised factors involved. Also isn’t much of the VLBA in the northern hemisphere, when much of the southern Milky Way (and the galactic centre) is not very well placed. Some work like this is conducted with the “Australia Telescope” – where the… Read more »
Silver Thread
Member
Silver Thread
January 5, 2009 8:26 PM

Salacious, your an inflammatory troll with an inferiority complex large enough to overshadow most of your ego, regrettably at least enough of that ego glares through that the rest of us are forced to squint in order to see past it and glean the quanta of useful material you may have posted.

Consider letting those big old chips slide off your shoulders and act like an adult. National boundaries don’t dissect the heavens and we all get to look at the same sky, even if we then choose to share a discussion about in on an American Based Website.

James
Member
James
January 5, 2009 8:59 PM
There are these things called a “Globe” – “Astronomy Software” – “Map” – “Google” and more! Try them, Hawaii and the Caribbean are well situated to view the galactic center, oops that’s American, centre if you prefer. We apologize for having “..best resolving power, of any astronomical tool in the world. ” It was a mistake, sorry it offended you or inflamed your hatred of us. We will attempt to dismantle the resolving power of all our telescopes to be less than the “Australian Telescope.” We’ll get on that metric thing asap. Why do you think the authors of this site use “American” miles? You would think their target audience would be Australians. There has to be more… Read more »
Salacious B. Crumb
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Salacious B. Crumb
January 5, 2009 9:02 PM
Ah! Silver Thread, I was wondering when you were going to come back with your usual dazzling insight. Good to see, as usual, your continued fascinating interest in the subject matter and your dissemination of knowledge. Frankly I really do take to heart your often penetrating and razor-sharp opinions. I’m so amazed you can so quickly adjudge my own personality or my status of my ego – more so as I don’t happen to know you at all? As to being “forced to squint”, I so suggest you visit your local optometrist, as from my point of view, I can read it perfectly. Thanking you again for your usual sensitivity and savvy farsightedness. Note: The IAU astronomical standards… Read more »
Peter
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Peter
January 5, 2009 9:10 PM

Salacious,

How can a difference in speed of 20% be reflected in your 223 to 226 kps math?
Methinks the man that correcteth, should correcteth correctly.

Salacious B. Crumb
Guest
Salacious B. Crumb
January 5, 2009 9:29 PM

Could to see how quick you can find such errors. Makes me wonder why it needed to be converted in the first place, don’t you think? Funny. I think I’ve just made my point.
Note: Actually it is 268 and 226 k.sec^-1, respectively.

Salacious B. Crumb
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Salacious B. Crumb
January 5, 2009 9:59 PM
Bosco, I think you totally miss my point. It has nothing to do with assumed “inflamed your hatred of us”, because my point is towards the portrayal of issue. The many Americans at this interesting conference are not dumb at all. As a science, astronomy is supposed to a universal science without borders or nationalities. Much of the work being presented at the American Astronomical Society are in fact great collaborations of many astronomers from all parts of the world. As such, the universality of astronomy should be projected through agreed standards, both in terms of units of measure and in their results.’ This “Mine’s better than yours” is not my attitude or point at all. Astronomical facilities… Read more »
Salacious B. Crumb
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Salacious B. Crumb
January 6, 2009 12:03 AM

Bosco
I carefully re-read your tirade against me again… but there is a much better point, though…

It is the “International Year of Astronomy: 2009” and not just the “American Year of Astronomy: 2009″

Also it would help to use the names of the spokesman I.e..”Mark Reid of the Harvard-Smithsonian Center for Astrophysics” AND the names of the collaborators. (As shown above, it was far from just the Harvard-Smithsonian Center for Astrophysics. Perhaps the looser use of “collaboration”, as by Nancy here, should also be promoted or focussed on at this AAS Conference.
Both the American and the other contingents should be proud of what they heave learned – but remember it is the ;
“INTERNATIONAL Year of Astronomy : 2009

LLDIAZ
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LLDIAZ
January 6, 2009 7:12 AM

You all seem very intelligent to me as far as grasping the basics of the term at hand but I find the true “measure” of intelligence is understanding the most complex material and then explaining it in a way that anyone else could understand it.

Salacious B. Crumb
Guest
Salacious B. Crumb
January 6, 2009 7:22 AM
After some extra research into this interesting issue – especially as some probably deem me as a bit of a ‘ratbag’, but it is interesting to compare this article with the official Harvard-Smithsonan Centre of Astrophysics in the CfA Press Release No. 2009-03 and also at NRAO It is poignant that the following consecutive quotes appeared in this press release but does not appear in the article here. “The new VLBA observations of the Milky Way are producing highly-accurate direct measurements of distances and motions,” said Karl Menten of the Max Planck Institute for Radio Astronomy in Germany, a member of the team. “These measurements use the traditional surveyor’s method of triangulation and do not depend on any… Read more »
Trevor
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Trevor
January 6, 2009 2:13 AM
I wonder if aliens will take offense when we use the parsec as a measurement of distance during the Universal Year of Astronomy, 2509… You know, that would be WAY too Earth-centric… Units of measurement don’t indicate nationality, but a prejudice against a unit of measurement may indicate a prejudice against a nationality, or perhaps just a large ego combined with an inferiority complex. I’m sure anyone capable of understanding the concept can convert units of measurement at will, rendering the actual choice of units trivial. Back to real business; let’s allow the scientists to sort out who gets the credit, if they even care. Unless any of us are part of the experiment or analysis, we should… Read more »
qraal
Member
January 6, 2009 2:18 AM

The conversion factor is 44.704 km/s for every 100,000 mph (i.e. 160934.4/3600.) Thus the old measure for rotation (492 kilomiles per hour) is actually 220 km/s. The new is 254 km/s (568 kilo-mph.

ScarfaceEd
Guest
ScarfaceEd
January 6, 2009 3:32 AM

Just some reflection:
600,000 miles/hr is about a 1000th of the speed of light. Our fastest spacecraft reaches 1/10,000th of c, 10 times slower than our sun…
If we were able to push on the breaks, we could reach stars that are behind us ten times faster.
Star trek is so far away…

Smapdi
Guest
Smapdi
January 6, 2009 3:51 AM

I want a pony. Please get me one.
Thanks

Salacious B. Crumb
Guest
Salacious B. Crumb
January 6, 2009 4:00 AM
Trevor, An Interesting assumption in saying; “I’m sure anyone capable of understanding the concept can convert units of measurement at will, rendering the actual choice of units trivial.” I can roughly do the maths in the head for miles to km, but not so much the other way around . As for gallons to litres, or vice versa – well got no idea, The main reason “Units of measurement don’t indicate nationality” is exactly why SI units are universally adopted by astronomers in the first place! – and the IAU thinks so too. The reason is that conversions are not necessary, and all units are mostly directly related in units or powers of ten. As for “or perhaps… Read more »
Paul Eaton-Jones
Member
January 6, 2009 4:03 AM

Personally I prefer m.p.h even when it’s 600,000. I know at that speed it’s almost immaterial what you use but I can get more of a handle on 50 m.p.h. than if it were expressed in km/s. I’m sure most scientists travelling in their cars would feel the same.

Salacious B. Crumb
Guest
Salacious B. Crumb
January 6, 2009 4:24 AM

Paul Eaton-Jones said;
“Personally I prefer m.p.h even when it’s 600,000. I know at that speed it’s almost immaterial what you use but I can get more of a handle on 50 m.p.h. than if it were expressed in km/s. I’m sure most scientists travelling in their cars would feel the same.”

OK, but how’s this for a radical idea. Why not print BOTH and avoid any possible confusion?

Paul Eaton-Jones
Member
January 6, 2009 4:32 AM

I’ll go along with that.

techqc
Guest
techqc
January 6, 2009 4:32 AM
“…we’re moving at about 600,000 miles per hour …” 600000 mph (rotation – verifiably so ?) “High-precision measurements of the Milky Way disclose our galaxy is rotating about 100,000 miles per hour faster than previously understood.” Rotating in reference to what ? A useless scalar in a cosmos of undefined vectors. Critical analysis of their data by someone with less ego-centric (culturally-centric) perspective might actually yield some credible insights it their data-acquisition methods are not also skewed by their academic religion. Still, it is an interesting story to read, even if it considers distance and time using hilariously different measurement units. They need that ‘yardstick’ to measure the miles between the hours they count over the light-years between… Read more »
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