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

Article written: 5 Jan , 2009
Updated: 24 Dec , 2015


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

30 Responses

  1. Venkatesh.S says

    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?

  2. Salacious B. Crumb says

    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 galactic centre and the other half of our Galaxy resides. Clear 17 of the 19 points shown are towards the galactic centre – are are northern hemisphere radio telescopes so good that they can peer through sold rock?

    Also moreover, please, please use the IAU standard units of kilometres per second and not the almost useless imperial measure as most of the (astronomical) world doesn’t use this antiquated measure
    Here, for example, the velocity of the Milky Way is spinning at “100,000 miles per hour” faster, should really read 27.7 kilometres each second. (I know 100,000 mph seems more impressive, but 160,000 kph is even better!)

    Other conversions for the rest of us ninnies…
    “600,000 miles per hour in our Galactic orbit, up from the previous estimate of 500,000 miles per hour.”

    Should in fact read;

    “226.2 kilometres per second in our Galactic orbit, up from the previous estimate of 223.5 kilometres per second.
    “28,000 light-years” is 8.6 kpc (kiloparsecs) in galactic terms, or 8,600 parsecs.

  3. Silver Thread says

    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.

  4. Bosco says

    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 “ 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 smart Australians in Alice Springs than smart Americans altogether! We are so dumb. Again we apologize for existing.

  5. Salacious B. Crumb says

    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 are in SI units not imperial units. America, or elsewhere, this is what has been internationally agreed upon. It might be inconvenient, but, well, that’s how it is.

  6. Peter says


    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.

  7. Salacious B. Crumb says

    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.

  8. Salacious B. Crumb says

    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 worldwide are shared by the whole international community to a fairly high percentage when it come to availability. In fact, many American astronomers do use and produce results with the radio “Australia Telescope” as well.

    As to; ” Why do you think the authors of this site use “American” miles?” Good question. Could it be because of the particular journalistic style of this article, perhaps?

    Actually, the information within this article is based on a paper of the Springer book of the Astrophysics and Space Science Proceedings; being”Mapping the Milky Way and the Local Group” (2008). “The scientists” (as this article says) are in fact;; Mark Reid, Andreas Brunthaler, Xu Ye; Zheng Xing-Wu, Karl Menten, Lincoln Greenhill and Luca Moscadelli.
    The affiliations of these collaborators are :
    Joint Institute for VLBI in Europe
    Max-Planck-Insitut für Radioastronomie
    Shanghai University,
    Nanjing University,
    Harvard-Smithsonian CfA)
    and Arcetri Observatory

    You can’t get more universal than that.
    So if is the case, why not mention this is an international collaborate, rather, as the reader will probably assume, American astronomers alone?

  9. Salacious B. Crumb says

    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

  10. LLDIAZ says

    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.

  11. Salacious B. Crumb says

    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 assumptions based on other properties, such as brightness, unlike earlier studies.”
    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.
    “These direct measurements are revising our understanding of the structure and motions of our Galaxy,” Menten said. “Because we’re inside it, it’s difficult for us to determine the Milky Way’s structure. For other galaxies, we can simply look at them and see their structure, but we can’t do this to get an overall image of the Milky Way. We have to deduce its structure by measuring and mapping,” he added…

    Surely the missing tid-bit from Karl Mentene is important, and although paraphrased by Nancy, misses the point that he was from Max Planck Institute for Radio Astronomy in Germany.

    Should Nancy be ceremoniously condemned for this – well actually not at all…

    The actual release was; “…issued jointly with the National Radio Astronomy Observatory. The National Radio Astronomy Observatory is a facility of the National Science Foundation, operated under cooperative agreement by Associated Universities, Inc.” – presumably the funding body and the facilitators of the instruments used. All, of course, American institutions and associated bodies. They funded so they deserve the kudos.
    However, who IS at fault is those first issuing the statement here. who have just watered down and spoon-feed it to the American public. In the end, the missing words are simple; by saying;
    “…the INTERNATIONAL team from xyz is conducting a long-term program to measure distances and motions in our Galaxy.”

    This gains the necessary support for the significant American contribution here, and decent prestige for their willingness for international co-operation and sharing the spoils. To me this is a a win-win situation.

    Yet it seems to me that only reason they didn’t do this is the perception by the Harvard-Smithsonian Center for Astrophysics press were fearful of negative consequences of appearing to the wider community as being somewhat un-American by doing so. If so, its a real pity they did, as all it leaves the American community just that little more isolated and insular, whose single-handed unilateral decision is almost against itself.

    As for the metric v. imperial debate, well the fault for this as well is also not actually Nancy’s, as the same press release coughs up the just same numbers.

    Whilst the material is admittedly written for general consumption, it would not have been too inappropriate to jazz-up the text for a bit more astute and clued-in readership. If there is an criticism, then maybe it is to be sensitive to the contributors to the story as well as the story itself, and perhaps adopt the AAS’s guidelines and present metric and imperial measures just to satisfy the broad nature of the audience.

  12. Trevor says

    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 stick to enjoying the data and the concepts.

  13. Adam says

    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.

  14. ScarfaceEd says

    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…

  15. Smapdi says

    I want a pony. Please get me one.

  16. Salacious B. Crumb says

    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 just a large ego combined with an inferiority complex.” is really not the issue. Complex issues and ideas need to be portrayed simply so that the message is not lost in the translation.
    As to “let’s allow the scientists to sort out who gets the credit” is perhaps a little shallow. My tax dollars in Australia go to funding the “Australia Telescope”, when some foreign astronomer uses it, it is my dollars what enable it to be achieved. When an Australian astronomer uses the VLBA, then you are paying for it with your own tax dollars then helps instead. It is a reciprocal relationship, an because the study of astronomy and astrophysics is often well beyond the Earth, what we learn benefit all in the world and not some petty nationalistic agenda. If one of my country’s astronomer contributes to some discovery, I’d like to know about it. If that astronomer happens to be an American – so be it, but don’t hide al those who happened to prop them up. If this is unacceptable, then let’s just change 2009 to “Year of Astronomy” and all of us not “play ball” – but I believe we’re much better than that.

  17. Paul Eaton-Jones says

    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.

  18. Salacious B. Crumb says

    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?

  19. Paul Eaton-Jones says

    I’ll go along with that.

  20. techqc says

    “…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 satellites lost to that fruit-basket measurement system.

    “The VLBA can fix positions in the sky so accurately…”

    accurately? ROFL

  21. Mr. Obvious says

    Salacious’ brain, enlarged “roughly” 4,000,000,000 times —–>.

    First of all… there is no “international” measuring standard for things. Nor is there a standard on what power you use when you do define a variables value. Don’t blurt out crap you don’t have any idea about. The IAU doesn’t insist on the use or endorse any system.
    If you were a real scientist/scholar you would realize this, since you would have read many papers, reports, thesis, outlines, blah blah, and noticed …. THERE IS NO STANDARD when it comes to UNITS OF MEASURE.

    Second… Salacious in your attempt to appear more intelligent than everyone, you actually appear more foolish. An intelligent person wouldn’t complain about what standard is used, because they are intelligent enough to convert it, and would even relish the challenge! If they didn’t know… they would welcome learning it. This should be obvious to anyone with “common sense”.

    Third… Only a bigot would keep belting out how any one country is the dominant feature here. Since you can’t open your mind beyond your own beliefs. I don’t think most people really care whether its the international year of astronomy, or the year of the blister. Just because an announcement was made in America doesn’t mean there wasn’t world wide cooperation; as is the case here. In fact, very few astronomical devices are used solely by one country. All most all are shared with scientist througout the world.
    Like anything else, if you have the money, you can use it. Your Aussie dollars also go to paying for an Aussie scientist to use the Keck scope in America. I could go into more detail here, but you have your own predjudiced belief which isn’t’ going to change.

    Fourth… this is an open blog. Full of experts and laymen alike. If you want something more precise and professional, then fork out 14,000 euros a year to join a professional organization and blurt your rediculous ramblings on its web site.

    Fifth… I’m sure you heard this a lot…. but everyone is aware what you are. You aren’t brilliant in any sense of the word. You are simply an idiot who has to bring up controversy in order to bring sunshine on your face and get noticed; just like a 4 year old attempting to get attention.

    You rant and rave about everyone else, yet for someone who bats down others unprofessionalism, you bring up everything in rants without using any objective reasoning or objective language. You simply site narrow views which are unfounded and unscientific in nature. Instead of being the all knowing jerk; if you really are knowledgeable you would spend your time helping others… instead of failing in your attempt to be superior.

    You can deny this all you want, but you can’t change our scientific, unbiased, and totally objective reasons for ‘knowing’ this. I’m sure you’ll now attempt to deflect all this by rambling back some more BS… but we have science; you only have bad methods!

  22. Salacious B. Crumb says

    Mr. Obvious,
    Thanks for you very much for your carefree appraisal, it is very much appreciated.

  23. Dan says


    Why don’t you take a bath and get all that Sand out of your vagina.

    Let us read through the well thought out and enjoyable comments/criticisms, not your usual negative and quite franky boring tirades.

  24. marcellus says

    I can convert miles into kilometers and vice versa, and I am just a humble forestry worker who’s winning the battle against global warming.

    This is a very cool story about our Milky Way Galaxy!

    Mr. Salacious should crack a Foster’s and just chill.

  25. Bosco says


    Ya, it would be a better point if after subtracting personal hallucinations the article had mentioned an “American Year of Astronomy.”

    Another point for you and others is this site is geared for laymen. Americans in particular. Why? Because it’s their largest audience. My guess, this is why miles are used. OR … it’s what the source material uses.

    Along those lines of being for laymen. They source the article to a CfA press release. You source it beyond that to a source not listed in their source. Assuming you correctly sourced it closer to, or to it’s original published source, we can

    Having followed up, as far as my interest allows, on your sourcing may it be asked, did you read the material and by doing so happen to notice all the contributers or where you chiefly interested in the contributers? How did you gain access to the original paper? Personal account, academic / institutional account or ? 25$’s a pop in offensive American dollars, why can’t they price this in Australian dollars or Euro’s, Yen, Pound, Peso, Dinar, Sand Dollars and Glass Beads? It’s soooo unfair. But I digress. It must be a bit expensive whatever currency.

    So you read the original paper, meant your approval? Good, Good, so uh … why are you here?

  26. Marco says

    600,000 mph…NASCAR eat your heart out.

  27. joe says

    When should we expect the first gravitational stresses from Andromeda that will begin to distort our galaxy? Do I have time for a last drink or two?

  28. Average Dad says

    All seriousness aside – does this mean that the Universe Song (Monty Python’s: Meaning of Life) will have to be re-written?
    Once again, I believe, the cosmos we live in surprises and educates (?) us.

  29. RUF says

    To the point at hand….

    Am I right in understanding we are now back to four galactic arms, instead of two? I know recently it was suggested we had 2 instead of 4.

    PS: I like m.p.h. (being American) but it is ok to put them in parenthesis after units. I would rather debate 4 arms or 2 arms rather than debate Imperial or Metric units!

  30. kts says

    I believe the reason why some stars follow an elliptical orbit around the galaxy is because our galaxy is a mixture of two galaxies that combined billions of years ago, would also explain why the two pairs of “arms” are not the same age too.

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