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
(Score: 2) by c0lo on Thursday March 15 2018, @08:28AM (9 children)
"the discovery that all disk galaxies rotate about once every billion years, no matter their size or mass.". Really? You really mean all?
" the researchers measured [...] in the outer disks of a plethora of galaxies" - so actually is not quite all, only a plethora of them. Is a plethora larger or smaller than a kilo-bunch?
"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." - so that plethora leaves enough room for a selection bias, which means it's less than a "statistically representative set".
Mmmmm... I see.
https://www.youtube.com/watch?v=aoFiw2jMy-0 https://soylentnews.org/~MichaelDavidCrawford
(Score: 3, Funny) by cocaine overdose on Thursday March 15 2018, @08:39AM
(Score: 4, Informative) by takyon on Thursday March 15 2018, @08:47AM (1 child)
The abstract pretty much agrees:
Gyr = gigayear = 1 billion years.
[SIG] 10/28/2017: Soylent Upgrade v14 [soylentnews.org]
(Score: 2) by DannyB on Thursday March 15 2018, @05:54PM
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.
What doesn't kill me makes me weaker for next time.
(Score: 0) by Anonymous Coward on Thursday March 15 2018, @09:23AM (3 children)
How did they manage to fail to remove the selection bias?
1. Take sufficient large sample size
2. Have a computer randomly select galaxies based on the number in 1
Measure ALL those galaxies.
(Score: 3, Insightful) by PiMuNu on Thursday March 15 2018, @10:56AM (2 children)
> 1. Take sufficient large sample size
You can only measure what you can see. The galaxies need to be side on to do the measurement, need to be visible, etc.
(Score: 0) by Anonymous Coward on Thursday March 15 2018, @11:19AM (1 child)
That would suggest that the authors think that there is a correlation between orientation, visibility and other selection criteria (compared to our galaxy) and the rotational speed. I doubt that such correlation would exists.
(Score: 2) by PiMuNu on Friday March 16 2018, @10:58AM
> the authors think that there is a correlation between orientation, visibility and other selection criteria
No, it means the authors cannot exclude such a correlation. They can't exclude such a correlation because they can't measure the galaxies that they can't measure.
(Score: 0) by Anonymous Coward on Thursday March 15 2018, @09:51AM (1 child)
Lando broke the hyper drive. Thats why
(Score: 0) by Anonymous Coward on Thursday March 15 2018, @11:19AM
It's not my fault!
(Score: 2) by TheLink on Thursday March 15 2018, @09:02AM (3 children)
When stuff is that big does the speed of light become significant for rotation calculations? e.g. stuff further away is not actually being attracted to the center but to different places due to the lag. 50,000 light years from the center while some galaxies are supposedly moving at speeds of 70 to 600km/sec ( https://astrosociety.org/edu/publications/tnl/71/howfast.html [astrosociety.org] ). My naive calculations 50000 years * 600 km/sec ~ 100 light years ~ 0.2% of 50,000 light years.
How is this taken into account in the calculations for predicting galaxy rotation curves? Or does it not matter or is not significant?
(Score: 1, Interesting) by Anonymous Coward on Thursday March 15 2018, @11:24AM
I guess that depends on what you define as "significant for rotation calculations". Of course the Doppler formula for light depends on the speed of light, therefore it certainly enters in a significant way. OTOH, the absolute movement of the galaxies simply cancels out when you subtract the speeds of the two edges. It probably affects the error bars, though.
(Score: 2) by DannyB on Thursday March 15 2018, @01:44PM (1 child)
They all share a single common, non-localized drive shaft.
What doesn't kill me makes me weaker for next time.
(Score: 2) by bob_super on Thursday March 15 2018, @06:43PM
Well over three quarters of the population agrees that drive shafts and transmissions are a kind of black hole they'd rather not try to figure out. "By some miracle, that shit works, just tell me when it's time for maintenance"
My question would be how you managed to lose the oil cap for a supermassive black hole.
(Score: 0) by Anonymous Coward on Thursday March 15 2018, @09:28AM (3 children)
I'm surprised they could accurately measure this.
Let's say I look at a galaxy far away at T0, locate the points I want to measure and repeat the measurement at T1. Let's say the interval is 1 year, I would expect that T1 looks a lot like T0 (within error margins?) At best I would expect a point to move only a tiny fraction of a degree. This is separable?
(Score: 5, Informative) by deimtee on Thursday March 15 2018, @09:40AM (1 child)
You measure galaxies that are edge on to you. One side will be rotating towards you, the other away. You measure the diffference in the redshifts to get the rotational speed.
Then you just need to know how big the galaxy is to work out the rotational period.
If you cough while drinking cheap red wine it really cleans out your sinuses.
(Score: 0) by Anonymous Coward on Thursday March 15 2018, @10:17AM
Thank you for the clarification.
(Score: -1, Troll) by Anonymous Coward on Thursday March 15 2018, @10:11AM
both reason and logic say that any statement like that has to be false.
statistics and physics are sitting in the corner crying when that happens.
so, no. this is not determinable by day-flies like us.
it would seem meant for children at best.
(Score: 1, Troll) by Bot on Thursday March 15 2018, @12:53PM
I thought the matter was settled back in 2007
https://www.youtube.com/watch?v=bhSB8EEnCAM [youtube.com]
Account abandoned.
(Score: 3, Funny) by nitehawk214 on Thursday March 15 2018, @04:54PM
I guess that throws out the watchmaker argument.
"Don't you ever miss the days when you used to be nostalgic?" -Loiosh
(Score: 0) by Anonymous Coward on Thursday March 15 2018, @09:39PM (1 child)
Whereas if you sat in the middle you'd go all the way around in less time?
(Score: 2) by Lester on Thursday March 15 2018, @10:33PM
Yes, a rotating galaxy is not like rigid disc, it is more like a whirlwind, the center spins faster, and outer side is dragged and falls behind. That why galaxies have such spiral shape
(Score: 0) by Anonymous Coward on Thursday March 15 2018, @10:51PM
1. Do we play them from the edge in, or the centre out?
2. Do we use a Gravimetric or an Optical pick-up?.