Astronomers unveil most detailed map of the Milky Way to date

[Sensei]

Hello!

 

"Astronomers unveil most detailed map of the Milky Way to date"

http://sci.esa.int/star_mapper/

 

https://www.theguardian.com/science/2016/sep/14/astronomers-milky-way

 

Best Regards!

Edited December 7, 2016 by Sensei

[Phi for All]

Thank you for sharing that, Sensei. That's amazing!

[michel123456]

Nice.

 

But i get the feeling that it may give a false impression. It shows a lower concentration of stars as you go out. Does that mean that the concentration is lower, or that the closest stars are hiding a whole bunch of stars behind them?

 

When you drag the pointer from here to there and make it rotate, you can even feel as if there were a radial organization. There is no such a thing, simply the missing stars are radially organized because they match our line of sight.

I think.

 

 

[Mordred]

good link thanks

[Janus]

 

Nice.

 

But i get the feeling that it may give a false impression. It shows a lower concentration of stars as you go out. Does that mean that the concentration is lower, or that the closest stars are hiding a whole bunch of stars behind them?

Screen Shot 12-08-16 at 08.32 PM.JPG

 

When you drag the pointer from here to there and make it rotate, you can even feel as if there were a radial organization. There is no such a thing, simply the missing stars are radially organized because they match our line of sight.

I think.

The "missing" stars are just those whose apparent magnitude are below the detection threshold. We can't map all the stars even in the mapped region because some are just to small and dim to detect. The further away a star is the brighter it has to be to be detectable. Therefore a B class star can be easily be detected at 1000 light years, but a G class star would have to be much closer and an M class even closer. And since the relative percentage of the population is higher for low mass dim stars than it is for high mass bright ones, you are going to see an apparent drop in star count as you look further away.

Edited December 9, 2016 by Janus

[AbstractDreamer]

1,000,000,000 stars.... 1% of milky way. I'm speechless.

 

We're SO not alone.

 

Or god created way more than he needed.

 

There I was worried about heat death. I feel safer already.

 

Would other galaxies show up within apparent magnitude 13.3, but distance is too far to plot?

 

What is the apparent magnitude of the brightest galaxy? Would that be Andromeda?

 

And another 100,000,000,000 galaxies in our observable universe?

Edited December 9, 2016 by AbstractDreamer

[michel123456]

The "missing" stars are just those whose apparent magnitude are below the detection threshold. We can't map all the stars even in the mapped region because some are just to small and dim to detect. The further away a star is the brighter it has to be to be detectable. Therefore a B class star can be easily be detected at 1000 light years, but a G class star would have to be much closer and an M class even closer. And since the relative percentage of the population is higher for low mass dim stars than it is for high mass bright ones, you are going to see an apparent drop in star count as you look further away.

Well understood.

But I was suggesting that some stars may hide other stars behind them. Or am I completely wrong?

[Janus]

Well understood.

But I was suggesting that some stars may hide other stars behind them. Or am I completely wrong?

Remember, those little circles in the map are not representative of the actual star sizes.

Let's take Sirius for example of how likely it is for a star to hide another. At 8.6 light years away and 1.7 times the radius of the Sun, it is going "hide" a area of ~1.1e-26 square degrees of the sky behind it. At 1000 light years, with an average distance of 3 light years apart, you will get ~ 1 star per .073 square degrees. This makes the chances of Sirius blocking any star 1000 light years away is 1/6.6e24. Of course there are other stars in between 1000 light years and Sirius' distance it could block, but as you consider each "shell" of stars closer to Earth, the further they are spread out from each other in angular distance. At 500 light years, the stars average angular distance apart doubles and the angular area per star increases by a factor of 4 ( the chances of Sirius blocking the view of a star 500 light years away is 1/4 that of one 1000 light years away. )

But even ignoring that and assuming a constant chance for blocking any star for any distance, At an average 3 light year distance part, ~333 "shells" of stars fit between Earth and 1000 light years, and 6.6e24/330= 2e1022, and you end up with the chances of Sirius blocking any star behind it out to 1000 light years as being 1/2e22. And that's for a nearby star. The further a star away is, the smaller its angular size as seen by the Earth, and the lower the chances of it hiding another star behind it.

But even if every star had an equal chance of blocking a star behind it(1/2.2e22), with 1,000,000,000 stars, the chance are only 1/2.2e13 that any star is hidden by another star.

 

So even if my estimate is off by several magnitudes, the number of stars likely to be hidden by other stars is going to be too small to cause a noticeable difference in this map.