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midtskogen
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29 Jan 2019 22:09

NIL DIFFICILE VOLENTI
 
Terran
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30 Jan 2019 08:49

All of the news as of late has been headlines saying “Universe expanding faster than thought” but after a few days and many sites later, including nature, none of them has said this new rate. What is the measurement! I have to know!
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Watsisname
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30 Jan 2019 09:31

Terran wrote:
Source of the post All of the news as of late has been headlines saying “Universe expanding faster than thought” but after a few days and many sites later, including nature, none of them has said this new rate. What is the measurement! I have to know!

The expansion rate of the universe is the "Hubble Constant", with units of kilometers per second per megaparsec.  The new value of expansion rate being reported isn't actually "new", but a discrepancy between two different methods of measuring it, and such discrepancy has a very long history.

In brief, measurements using the Cosmic Microwave Background radiation place the value of the Hubble constant at somewhere around 67km/s/Mpc, while a an analysis of type Ia supernovae place it higher, at around 73.5km/s/Mpc.  There are error bars associated with both of these values, but they don't overlap, so the measurements conflict with each other.  

I describe the history of measurements of the Hubble constant, and some of the implications of what this higher value could mean, here in the Cosmology Thread, and there is also an excellent PBS Space Time video about it:

 
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Gnargenox
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01 Feb 2019 15:05

A Chelyabinski or meteorite impact hits a town in Western Cuba.
https://www.rt.com/news/450362-meteorit ... ba-photos/
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Watsisname
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01 Feb 2019 15:24

Neat.  The claimed meteorites shown in the pictures look like the real thing, with fusion crust.

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A-L-E-X
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02 Feb 2019 04:25

They said it was the biggest strike in over 100 years?  I wonder if thats really true
 
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midtskogen
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02 Feb 2019 09:28

Definitely the right stuff.  I think it's too early to judge how it compares with Chelyabinsk.

What if this had happened during the Cuban missile crisis...?
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02 Feb 2019 10:39

I just heard, no reference, that it exploded with 1% the force of the Chelyabinski explosion.
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Watsisname
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02 Feb 2019 12:16

midtskogen wrote:
Source of the post What if this had happened during the Cuban missile crisis...?

Terrifying to contemplate.
 
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05 Feb 2019 21:01

The Atacama Large millimeter/submillimeter Array discovered an unusual planetary system orbiting the 2 to 2.5 million year old T Tauri star CI Tau. The young star 518 light-years in the Taurus constellation had gained prior notability from astronomers when they discovered the first hot Jupiter orbiting such a juvenile star in its protoplanetary disk. Since then, three other gas-giants were detected. The two outer planets have masses comparable to that of Saturn, the new inner one has roughly 1 Jupiter mass.
 

Also, (mind you this was back in November) the renown cosmological Hubble's Law has been renamed the Hubble-Lemaitre in an IAU vote? Apparently the original name didn't commemorate the somewhat obscure work of the Belgian priest Georges Lemaitre and his equations related to the expansion of the universe. I wonder if that name will stick - although double names are nothing new in astronomy :).
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Terran
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12 Feb 2019 10:31

Watsisname wrote:
In brief, measurements using the Cosmic Microwave Background radiation place the value of the Hubble constant at somewhere around 67km/s/Mpc, while a an analysis of type Ia supernovae place it higher, at around 73.5km/s/Mpc.  There are error bars associated with both of these values, but they don't overlap, so the measurements conflict with each other.  

I am pretty sure they recently tried a new method using quasars and found the expansion to be even faster, but I havent found any official values for this value.
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Watsisname
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12 Feb 2019 12:26

Terran wrote:
Source of the post I am pretty sure they recently tried a new method using quasars and found the expansion to be even faster, but I havent found any official values for this value.

Yeah, under the acronym "H0LiCOW", where they measure the Hubble constant from gravitationally lensed images of quasars.  The team has a nice short video explaining how the method works:



Combining the measurements of 4 such lensed quasars leads them to a value of 72.5km/s/Mpc, plus or minus about 2.2:

Image


The strength of this method is that it doesn't depend on the cosmic distance ladder, where we chain together several different methodologies of measuring distances, from short scales to longer.  In that sense this is a very independent form of measurement of the expansion rate.  The downside is that it does rely on knowledge of the geometry of the lens, and the amount of matter in the universe.  So to make the error bars as small as they claim, they need to combine their data with measurements of the matter density and curvature of the universe from Planck data.


This value is also only based on 4 objects, so the precision may continue to improve as more of these multiply-imaged quasars are discovered and studied. :)


Another independent measurement of the Hubble constant can be done from gravitational wave events, if the event is connected to a visible source, as was the case with the binary neutron star merger a couple years ago.  The gravitational waves tell us how far away the event occurred, and the electromagnetic observations tell us how much it was redshifted, so together this acts as a measurement of the expansion rate.  Unfortunately, with one event and large uncertainties on its distance, the error bars are huge and don't tell us "who is right" about the Hubble constant.  But again with more of these events detected in the future, they very well could help pin it down.
 
A-L-E-X
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13 Feb 2019 05:41

Watsisname wrote:
midtskogen wrote:
Source of the post What if this had happened during the Cuban missile crisis...?

Terrifying to contemplate.

Exactly why we need to ban all nukes worldwide outside of the ones that will be used to stop an ELE!
 
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15 Feb 2019 00:40

RIP Opportunity.

07/07/2003 - 13/02/2019.




The "Last Image":
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21 Feb 2019 18:01

It looks like some of Jupiter's moons are finally getting names by April 15. A naming contest was held by Carnegie Science where you can help suggest names for five of Jupiter's moons: https://carnegiescience.edu/NameJupitersMoons

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