Topic: Scientific Picture of the Week (another new feature)

[sam]

Following on from the announcement of this board we have another new feature that I'm going to hopefully try and maintain... a scientific picture and some description.. probably not just astronomy but this will be a major part of it...

I thought we would start of with black holes, which follows off nicely
from (http://www.pc-pals.com/smf/index.php?topic=25962.15), well not so much a black hole but the supermassive black hole at the centre of the Milky Way..



Image Credit:  Rainer Schödel (MPE) et al., NAOS-CONICA, ESO

This is not the most picturesque of astronomical images but probably one of the most striking ones for modern astrophysics. This deepnear-infrared image shows the crowded inner 2 light-years of the Milky Way (the exact position of the centre is indicated by arrows).These observations were part of a programme to track the stars around the blackhole have quite nicely proved that these objects exist. There was a time when this was some crackpot theory, now its pretty much accepted that all (large) galaxies have one at the centre.. some are "switched-off" and others are hungry beasts. The one at the centre of the Milky Way is over 2 million times the mass of the Sun (I'm unsure to the actual currently accepted value).

[GillE]

Nice picture, but how do you photograph a black hole?  I thought you could only tell it was there because of the way it bends electromagnetic fields and suchlike.

Incidentally, I've just finished reading a book which claims that the contents of a novel could be hidden in a photo like that!

[Simon]

It's so hard to even get your head around the scale of this stuff.  Presumably, we would be a microscopic dot somewhere in there?  This is why it's so hard to believe, that in the unimaginable vastness of the Universe, we are the only forms of life.

[sam]

Nice picture, but how do you photograph a black hole?  I thought you could only tell it was there because of the way it bends electromagnetic fields and suchlike.

Incidentally, I've just finished reading a book which claims that the contents of a novel could be hidden in a photo like that!

you are probably right about the novel in a picture like that! There must have been thousands of pages written about these photos now.

As for how to photograph a black hole, well this isn't really a photograph of the black hole, sorry I was a bit misleading in my text. This is a photo of the region around the central black hole. We don't even tell by the way it bend the light around it (that's gravitational lensing and that can happen around any mass, though to be noticeable it has to be fairly big.. and I guess the black hole does do that) but by closely monitoring the stars. If we take enough observations of the stars then we are able to deduce their orbit, just like Kepler did with the planets and determine the mass of the thing that is causing that orbit. By closely monitoring literally hundreds of stars at the centre of the galaxy we are able to appreciate the size and mass of the black hole.

[sam]

It's so hard to even get your head around the scale of this stuff.  Presumably, we would be a microscopic dot somewhere in there?  This is why it's so hard to believe, that in the unimaginable vastness of the Universe, we are the only forms of life.

1 light year is fairly small numbers. The nearest star from the Sun is (Clive might put me correct here, and no I'm not goign to include any random objects or possible dwarf stars) Proxima Centuri, some 4.22 light years away, some 390000000000000000 metres or 266 871.415 Astronomical Units (the distance between the Earth and the Sun). In this photo, I'm not sure you can actually see it, but the closest star to be going around the central black hole is going around with a orbital radius of 3 times that of the orbit of the dwarf planet Pluto.... so our solar system would be little more than a dot on that picture. Scary stuff really.

[Simon]

[Clive]

This is a truly awesome photo of the very centre of our Milky Way galaxy.  If you want to know which direction to look for it, look towards south on any clear night this month and you will see the very bright planet Jupiter.  After the Sun and the Moon, Jupiter is currently the brightest object in the sky.  A the moment, Jupiter lies in front of  the constellation of Sagittarius which is the direction of the galactic centre.  The black  hole at the centre can't be seen but we know it's there because the 10 million stars in Sam's photo are all orbiting it at breakneck speeds of 5 million kph.  Calculations show that in order for the stars to orbit at that speed the unseen object must have a mass of at least 2.6 million suns.   

[Simon]

It's just mind boggling, isn't it?

[GillE]

Very interesting explanation of how to observe a black hole, Sam - thanks.

It would appear my language wasn't terribly precise when I said "the contents of a novel could be hidden in a photo like that".  I meant it literally!  Apparently, by varying the pixels in a photograph that size just slightly, it's possible to conceal a whole book of text in the image.  Osama Bin Laden's lot has used that technique extensively in the past, especially in photos on eBay.  It makes you wonder, doesn't it?

[sam]

Very interesting explanation of how to observe a black hole, Sam - thanks.

It would appear my language wasn't terribly precise when I said "the contents of a novel could be hidden in a photo like that".  I meant it literally!  Apparently, by varying the pixels in a photograph that size just slightly, it's possible to conceal a whole book of text in the image.  Osama Bin Laden's lot has used that technique extensively in the past, especially in photos on eBay.  It makes you wonder, doesn't it?

Oh yeah, I've come across that before - I actually have a tool that can do that (somewhere) - its fairly simple stuff to break though.. so I wouldn't worry - but quite useful to hide stuff from prying eyes who have no idea.

[sam]

It's just mind boggling, isn't it?

yep, I find it very hard to fathom the stuff I do at times. I'm currently looking at radio galaxies that took the light 12.469 Giga years to get here! (and yep Clive we expect they are around z = 5, so an age of the Universe of just 1.197 Gyr)

[Simon]

I'm currently looking at radio galaxies that took the light 12.469 Giga years to get here!

Sounds like my local radio station's playlist!