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37
pdonis
> how do we know it isn't dark matter causing the collapse to happen faster than thought?
The average density of dark matter is way too small. It's significant on the scale of a galaxy because it doesn't clump, so its density is basically the average density everywhere (denser towards the center and less dense further out, but still of the same rough order of magnitude), instead of being isolated clumps surrounded by huge expanses of empty space, as with ordinary matter. But on the scale of a single stellar system the density of dark matter is so small that its effect on the dynamics is negligible.
treeman79
Good explanation of low density of dark matter as measured by squirrels.
37
This is a excellent response! Thank you!
dtgriscom
The observations didn't measure the speed of the collapse; they measured the strength of the magnetic field which guides models of the collapse. Magnetic fields tend to slow the gas collapsing, so finding that the fields were lower than expected decreases the expected time of collapse.
37
Thank you! This is also a great response! Now I'm wondering how they measure magnetic fields. But of course I'm sure there's about a million youtube videos explaining that.
>Magnetic fields tend to slow the gas collapsing, so finding that the fields were lower than expected decreases the expected time of collapse.
I think this part might be backwards, wouldn't it increase the expected time of collapse, which is to say stars may form faster than thought?
(edit: no, I'm just tired and wrong, yet again...)
antognini
At a very simplified level, in these kinds of astrophysical contexts you can kind of think of magnetic field lines as strings, and the particles in the gas are forced to follow the strings. The stronger the field, the more closely the particles have to follow those strings. So if the magnetic field is large, they can have the effect of redirecting particles from where they otherwise would go due to gravitational collapse, and slow the process down.
simonh
They explain the measurement approach in the article. The Zeeman effects occurs when spectral absorption lines 'split' due to the influence of magnetic fields. They measure this effect at radio wavelengths.
37
This led me to thinking, how do we determine the age of the sun? I would have thought some radio spectrometry, but according to NASA[0]:
>We look at the age of the whole solar system, because it all came together around the same time.
>To get this number, we look for the oldest things we can find. Moon rocks work well for this. When astronauts brought them back for scientists to study them, they were able to find out how old they are.
sokoloff
That led me down a “how did they date the moon rocks?” thread, which led me to this explanation: https://www.sciencealert.com/we-finally-know-the-precise-age...
37
>researchers say they’ve finally pinpointed the exact age of the Moon
Hmm, sounds dubious, but I will read on. A short while later it leads me to the paper[0] and I spend a few more minutes on that, finding myself asking: how do we know the zircon fragments aren't from a meteor that is much older? Surely all the fragments came from approximately the same area, yes? Or maybe not?
But nah, these knowledgeable astronomers must have already thought of all this stuff.
Astronomy is just filled with rabbit holes I guess.
pdonis
> how do we know the zircon fragments aren't from a meteor that is much older?
Radiometric dating tells you when the sample you are dating last solidified. Of course the atoms in the sample themselves existed before that, but that doesn't matter for radiometric dating since what is being measured is not the age of the atoms but the time the sample, the piece of rock you're analyzing, last solidified.
> Surely all the fragments came from approximately the same area, yes?
Um, yes, since the Apollo 14 astronauts only collected samples from a very small area.
> nah, these knowledgeable astronomers must have already thought of all this stuff.
Yes, in fact, they have, plus a lot more things that haven't even occurred to you.
kfarr
Just wait until you hear how astronomers date the approximate age of rabbit holes…
philipov
> Astronomy is just filled with rabbit holes I guess.
No wonder some cultures think Rabbits live on the moon.
politician
Isn't it kind of weird to use the Moon to benchmark the age of the solar system when it's well known that the Moon formed after another body collided with the Earth? The Moon is younger than the Earth.
treeman79
Moon is a mix of earth and theia. So is Earth. So sort of like a strawberry banana smoothie in two cups.
Core of Theia sunk into Earth and there is some recent imaging showing what may be the second core.
https://www.iflscience.com/environment/fragments-of-the-plan...
tshaddox
I assume it’s because the Moon is geologically inactive and thus the rocks we got from the surface are expected to be essentially as old as the Moon itself.
pdonis
Not to benchmark, precisely, but to give a lower limit on the age that will likely be longer than any other lower limit we could obtain at our current or near future level of technology.
vlovich123
If Theia is older than the Earth, then wouldn't the Moon also be older?
politician
AIUI, the heat of the collision would've melted everything that wasn't already molten. Any "age" information would be lost as the system cooled. At least, that's my understanding from playing with Universe Sandbox.
peter303
There was a hardcore "Revive Arecibo" workgroup at two recent astronomy conferences. That telescope made important data contributions up to the end, despite its age. Alas, probably a pipe dream, since NASA/NSF has limited funding for all the fantastic stuff in the pipeline already.
UncleOxidant
Maybe there's also a realization that the location isn't ideal in a time of increasing hurricane activity due to climate change?
glennonymous
Not a scientist. But if this is true, would it imply that A) the universe is younger than we thought, or B) there was a much longer time between the Big Bang and the formation of the first stars? Seems to have very major cosmological implications.
glennonymous
Upon five more minutes’ consideration, I thought of several reasons why this would probably not imply either of the things I suggested it might imply. But my larger question is: What, if any, would be the larger cosmological implications of this discovery?
tuatoru
Yes, according to this StackExchange answer[1] star formation was thought to take around 10 million years (for low-mass stars - less for big stars).
That would be a rounding error on a reasonably precise and accurate estimate of the age of the universe (which I don't think we have yet.)
As for cosmological/other physical implications, it's a "well, now we know more" result.
1. https://astronomy.stackexchange.com/questions/156/how-long-d...
omegalulw
> the universe is younger than we thought,
Not really. Don't we estimate the age of the universe by estimating how redshifted the CMB is compared to what we would expect given initial conditions?
37
One order of magnitude off doesn't seem too bad of an original prediction
smm11
So I might be able to notice a .00000001 percent change in my lifetime. Cool.
hsnewman
Then again, they may not form 10 times faster than thought.
dr_dshiv
I think I think faster than stars form, right?
bryanrasmussen
The ambiguity of the English language can often be lessened via simple changes, such as: Stars may form 10 times faster than generally thought.
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>But observations using the world’s largest radio telescope are casting doubt on this long gestational period. Researchers have zoomed in on a prestellar core in a giant gas cloud—a nursery for hundreds of baby stars—and found the tiny embryo may be forming 10 times faster than thought, thanks to weak magnetic fields.
I'm sure this has been taken into account already (by actual scientists much smarter than me) but, how do we know it isn't dark matter causing the collapse to happen faster than thought? Seems like a reasonable question to me. Lack of gravitational lensing?
(edit:) Also
>thanks to weak magnetic fields ... Zeeman effect etc
This is a bit questionable to me. I understand the Zeeman effect, or thought I did, but I don't understand how it can be thanks to a "weak" magnetic field.