Gaia space telescope discovers 55 'runaway' careening away from stellar cluster at 80 times the speed of sound

[Admin]

Using the Gaia space telescope, astronomers have observed 55 massive stars ejected from their home star cluster in the Large Magellanic Cloud at speeds equivalent to 80 times the speed of sound.

Gaia space telescope discovers 55 'runaway' careening away from stellar cluster at 80 times the speed of sound : Read more

 

[billslugg]

Be careful when simplifying for the new folks. There is no air in space. Thus no sound. They will get confused. Kilometers per second is better.

 

[Unclear Engineer]

Be even more careful - the "speed of sound "WHERE?

In space, there is only about 1 atom per cubic centimeter, so the mean free path to the collision with another atom is huge, and that distance is the minimum wavelength a "sound" can have, so an extremely low frequency.

But, how fast is that frequency transmitted? Based on temperature of about 6000K, the speed of sound would be about 19,000 mph. But, if it is plasma instead of neutral atoms, than it is more complicated. The speed of sound in the "solar wind" has been estimated at about 125,000 mph. See https://physics.stackexchange.com/questions/162184/what-is-the-speed-of-sound-in-space for a rather confusing discussion.

But, what the non-scientist writers of articles like this seem to be comparing to is the speed of sound in Earth's atmosphere at sea level and "standard conditions", which is 761 mph.

However, the "mach number" is really the speed at a particular location divided by the speed of sound at that location. So, saying that an airplane at 60,000 ft altitude is doing "mach 1" would mean that it is only going 660 mph, because it is colder there and the speed of sound is very dependent on the temperature in a gas.

So, please "science writers", just give us the actual speeds of whatever you are writing about, because you would have to go to a lot of work to even calculate the proper mach numbers for the situations you are writing about, and if you don't tell us what the speed of sound that you are using is, we can't tell within a factor of 1000 what you are saying. Unless we just assume you mean 761 mph whenever you say "the speed of sound".

 

[Torbjorn Larsson]

Seems it could help with ionization, since early galaxies barely produced enough escaping photons.

Be careful when simplifying for the new folks. There is no air in space. Thus no sound. They will get confused. MPH is probably better.

There are sound wave analogs in the densest molecular clouds, albeit inaudible even if you removed your spacesuit and irrelevant to compare speeds.

For an international public kilometer per second would be more reasonable, since we could compare with astronomical speeds. E.g. planets orbit stars with typical speeds of tens of kilometers per second, stars orbit galaxies with typical speeds in the low hundreds of kilometers per second and galaxies move in relation to each other with typical speeds in the high hundreds of kilometers per second.

Ejected at around 20 -30 km/s is typical relative speeds for stars, I would think.

 

[billslugg]

"For an international public kilometer per second would be more reasonable, since we could compare with astronomical speeds." = Torbjorn Larsson

Duly noted and corrected.

 

[Classical Motion]

If those system velocity ratios have merit, then wouldn’t the galactic velocity give us the cosmic dipole?