Our Milky Way Galaxy: Now Faster and More Massive!

By Eliza Strickland | January 6, 2009 10:18 am

Milky WayWe residents of the Milky Way can puff ourselves up with pride: A new study has discovered that our galaxy is more of a force to be reckoned with than previously realized. Astronomers said Monday that the Milky Way is more massive than earlier known, given new measurements showing that the Sun is moving at 600,000 miles per hour around the center of the galaxy, or 100,000 m.p.h. faster than past calculations suggested. The higher speed of the Sun means the galaxy must have more mass — about 50 percent more — so as to generate a stronger gravitational pull to keep hold of the Sun, as well as all its other stars [The New York Times].

The new calculation puts our galaxy’s mass about equal to that of the nearby Andromeda galaxy, which was previously thought to be bigger than the Milky Way, says lead researcher Mark Reid. “Previously we thought Andromeda was dominant, and that we were the little sister of Andromeda,” Reid said. “But now it’s more like we’re fraternal twins” [AP]. But although the estimate gives our galaxy some new bragging rights, it’s not all good news. Being bigger means the gravity between the Milky Way and Andromeda is stronger. So the long-forecast collision between the neighboring galaxies is likely to happen sooner and less likely to be a glancing blow, Reid said [AP]. Luckily, that collision still isn’t expected for 2 to 3 billion years.

The make their discovery, announced at the ongoing American Astronomical Society meeting, researchers used the Very Long Baseline Array, a combination of 10 radio telescopes stretching from Hawaii to the Virgin Islands. Researchers used the radio waves that effectively penetrate clouds of interstellar gas to examine bright star forming regions around the galaxy when the sun was at different places in its orbit. “We’re using trigonometric parallax. It’s essentially what surveyors do here on Earth,” [Reid] said. “If you know the length of one leg of the triangle and the angles between the legs, you can calculate all the lengths.” In this case, they make an observation of the same region at two different times of the year, creating a triangle out of the earth’s two positions and the star itself [Wired News]. Then they could determine the speed at which our sun is moving, and then the mass of the galaxy.

It’s difficult to get an accurate idea of the Milky Way’s appearance from our position within it, but the researchers say their measurements do add evidence to the picture of a galaxy with four spiral arms in total, two of which are “minor” arms that contain only newborn stars. Most star formation in our galaxy takes place in the Milky Way’s spiral arms — where gas is compressed, triggering the birth of stars. By measuring the distances to [star formation regions] that appeared to reside within the same spiral arm, the researchers were able to determine how tightly wound each spiral arm is and how many times it wraps around the Milky Way [Science News].

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80beats: Confirmed: Monstrous Black Hole Lurks in Our Galaxy’s Center
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Image: NASA

MORE ABOUT: Milky Way, stars, telescopes
  • Greg

    In the first paragraph you correctly state a reference point for the calculated speed “Sun is moving at 600,000 miles per hour around the center of the galaxy,”.

    However, in third paragraph, you fail to mention the reference for which speed you refer: “determine the speed at which our sun is moving,”

    So my point is, when you say speed, you must really tell us “relative to what”. The flaw in your argument is that you are assuming the center of the Milky Way galaxy is “fixed” and thus non-accelerating.

    So my question is, if you include the possiblity that the entire reference system is accelerating, doesn’t that throw off the entire neat little package of assumed circular motion for which you have inexplicitly assumed!

    Tell me how the speed measurement corrects for or accomodates an accelerating galaxy in an accelerating universe?

  • http://clubneko.net nick

    Well, the headline’s misleading because nothing has changed except our measurements. But anyway, in regards to what Greg has posted, considering this is the same article, paragraph 3 pretty obviously refers to how they calculated the statement in the first paragraph, which you already agreed was correct.

    And it’s an accelerating expansion of spacetime. There is no frame of reference for us outside of the visible portion of spacetime we reside in, so we can’t tell if the whole of spacetime is moving or not. We can just tell it’s expanding, because it’s moving away from us at an accelerating pace.

  • chilton

    um in response to greg “showing that the Sun is moving at 600,000 miles per hour around the center of the galaxy, or 100,000 m.p.h. faster than past calculations suggested. ” means that the speed is relative to the center of our galaxy in this article
    if they were to measure the speed of our sun relative to our universe they would find varying results bevcause our sun revolves around our galaxy at some periods our sun would apear to move away from the center of the universe faster then when our solar system is at its oppoisite end of our galaxy and moving towards the center of the universe thus showing a slower speed away from the center but getting the fine measurments out of the way is the best way to start measuring, 100,000 kms is a huge difference and will go a long way in the future in plotting speeds and points in the universe

  • Damian McSorley

    So to sum up if this new model is applied on a universal scale does this necessitate a rethink on the size of the universe and the speed of expansion (ps im new to this so please be gentle).

  • Francis Vessigault

    The Milky Way Galaxy is 120 000 light years in diameter and Andromeda is little bigger;
    160 000 light years diameter.
    The Milky Way contains 294 billion stars but Andromeda 406 Billion stars.

    but I agree that the Milky Way is little more massive than Andromeda due to Dark matter.
    The collision that will happen for the sister galaxies will create the giant elliptical galaxy Milkomeda.

    The 100 billion Galaxies were all created by Jehovah, the Lord for His Father Eloheim.

  • kenneth y.

    um…to chilton… its possible to calculate the acceleration eventually. since the black hole is theoretically the center of the galaxy…you culd possibly calculate it from there and etc. time relative to the black hole could be compared to time relative to the sun in our system…its a plausible idea -kenneth y. 16-

  • Relax Frankie

    What the #_! does Jehovah have to do with the galaxies colliding? I seriously don’t think what you believe will be around in 2 or 3 billion years. Why does a specific religion always have to be part of a discussion that’s based on a science article? Why isn’t it going to be one of the thousand Buddhas, Christ himself or 70+ virgins? Grow up dude, seriously.

  • Hector

    Well…. Jan Oort determined the speed to be 558,000 mph, which is technically only 42,000 mph different than the current being suggested. Also, why is it impossible to conceive that the speeds are changing depending on the sun’s position in the galaxy? I find the idea of sticking to a fixed speed erroneous and unscientific. The days of Ptolemy are over. Science must now dominate.


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