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All Disk Galaxies Rotate at a Rate of About Once Every Billion Years

posted by martyb on Thursday March 15 2018, @07:11AM   Printer-friendly
from the circular-argument? dept.

AnonTechie writes:

In a study published March 9 [PDF] in The Monthly Notices of the Royal Astronomical Society, astronomers announced the discovery that all disk galaxies rotate about once every billion years, no matter their size or mass.

“It’s not Swiss watch precision,” said Gerhardt Meurer, an astronomer from the International Centre for Radio Astronomy Research (ICRAR), in a press release. “But regardless of whether a galaxy is very big or very small, if you could sit on the extreme edge of its disk as it spins, it would take you about a billion years to go all the way round.”

To carry out the study, the researchers measured the radial velocities of neutral hydrogen in the outer disks of a plethora of galaxies — ranging from small dwarf irregulars to massive spirals. These galaxies differed in both size and rotational velocity by up to a factor of 30. With these radial velocity measurements, the researchers were able to calculate the rotational period of their sample galaxies, which led them to conclude that the outer rims of all disk galaxies take roughly a billion years to complete one rotation. However, the researchers note that further research is required to confirm the clock-like spin rate is a universal trait of disk galaxies and not just a result of selection bias.

http://blogs.discovermagazine.com/d-brief/2018/03/14/galaxies-rotate-billion-years/

[Source]: Astronomy.Com

[Also Covered By]: ZME Science

Original Submission

 
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  • (Score: 4, Informative) by takyon on Thursday March 15 2018, @08:47AM (1 child)

    by takyon (881) <takyonNO@SPAMsoylentnews.org> on Thursday March 15 2018, @08:47AM (#652844) Journal

    Really? You really mean all?

    The abstract pretty much agrees:

    HI-Selected galaxies obey a linear relationship between their maximum detected radius Rmax and rotational velocity. This result covers measurements in the optical, ultraviolet, and HI emission in galaxies spanning a factor of 30 in size and velocity, from small dwarf irregulars to the largest spirals. Hence, galaxies behave as clocks, rotating once a Gyr at the very outskirts of their discs. Observations of a large optically-selected sample are consistent, implying this relationship is generic to disc galaxies in the low redshift Universe.

    Gyr = gigayear = 1 billion years.

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  • (Score: 2) by DannyB on Thursday March 15 2018, @05:54PM

    by DannyB (5839) Subscriber Badge on Thursday March 15 2018, @05:54PM (#653020) Journal

    Gyr = gigayear = 1 billion years.

    So my standard answer still works:

    I'll get back to you on that in one quarter of a galactic turn, or right after I upgrade to Windows XP.

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