Author Topic: Sunday 22nd April 2012: ancient but still going  (Read 1029 times)

Alice

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Sunday 22nd April 2012: ancient but still going
« on: April 23, 2012, 02:08:04 am »
Today's Object of the Day is a nomination from paulrogers.


588017948808839288

Not much there you think? Let's zoom out and see if there's anything . . .



. . . hmmm, just some lines really . . .

Or, if you really want to take a peek around, expand this! I've made it 2048 by 2048 pixels and shrunk it here - click on it to enlarge. I think I spy a comet in the top left quadrant!



Still nothing much though.

Yet . . .

This small central object has just been in the news. Paul identified it not only by its coordinates but by its spectrum:





As he says: "That's what happens when a white dwarf cools to such an extent that the peak of its black-body radiation has entered the infrared.  How old is that, you may ask?"

So, it's a white dwarf, and he and Skyserver posted it in the Weirdest Spectra thread. SIMBAD appears to have given it a faulty z reading of 1.493 - that is, over 9 million light years away! But it's in our own galaxy (for it to be that far away yet still visible it would have to be a quasar, and its spectrum sure doesn't look like one).

As a matter of fact it is wandering around relative to us - but for a different reason. It's in our own galaxy. And it's very near us. Only 100 or so light years away.

It is also 12 billion years old!

This is one of the two ancient white dwarves in Ursa Major and Taurus recently discovered by astrophysicists at the University of Oklahoma. These were white dwarves when the Universe was under 2 billion years old - some seven billion years before our Sun and Earth were even born.

They are called WD 0346+246 and SDSS J110217, 48+411315.4 (J1102) respectively - this one of course is SDSS J110217, 48+411315.4 (J1102) and is located in Ursa Major. (There's a lovely website showing the polar constellations including Ursa Major here, and a rather unusual use of Ursa Major as a direction for a silliness break here.)


Ursa Major through the trees, photograph by Mike Peel, at the Astro blog at Strudel, 2009.

To understand how we know that it's an old white dwarf, we need to know about blackbody radiation. (I still find it confusing myself, but it's a pretty simple concept.) A black body is something that sounds like the opposite of a star - something that absorbs all radiation, whether it's radio waves or X-rays or light or heat or what, never mind its angle or anything else. It also emits radiation of different wavelengths - let's say a bit of heat (weakest), a bit of ultraviolet (strongest), and lots of light (in the middle). If we plot this on a graph, it'll be what we call a peak - it's like a tall hill. It might be leaning over to one side, but generally, you start low, go up, and then go down again.

You can work out the temperature of a blackbody by where this peak is. For most stars, it's in the visible light range. (It was the discovery of this kind of physics that ushered in the quantum revolution - Max Planck was a very traditional theoretical physicist and disturbed to find out that his results must mean energy is quantized, ie comes in small packets, rather than a continuous substance.)

Anyway, for these dwarves, as Paul points out, they peak in the infra-red range. They are quite cool. That means they have had a long time to cool down. A very long time. (Incidentally, white dwarves cool down so slowly that all of them are still radiating - there are no actually cold ones yet, the Universe isn't old enough!) And Kilic et al, the folks at Oklahoma, havce calculated the cooling time to be 11-12 billion years!

Since a white dwarf comes from a star, the stars had to be even older than that - a time when the Universe was really young! These stars - this very galaxy - must have formed pretty shortly after the Big Bang! All those frustrating faraway wisps we get in the Hubble pictures we classify - our Milky Way might have been that weird-shaped once upon a time!

It really brings home the idea that the Big Bang happened right where we are today. Yes, it happened as far away as we can see, too. It happened everywhere. And a part of it happened right at the electronic you're reading this on. What a mind-boggling thought!

You can read the press release here, the paper here (thanks Paul!), also at Science Daily, DNA, and a bunch more at EU Science News.
« Last Edit: April 23, 2012, 02:10:10 am by Alice »

egalaxy

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Re: Sunday 22nd April 2012: ancient but still going
« Reply #1 on: April 23, 2012, 02:48:09 am »
great OotD! 9 million light years? wow SIMBAD might wanna fix that one soon!

VJOM

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Sunday 22nd April 2012: ancient but still going
« Reply #2 on: April 23, 2012, 04:56:44 am »
by testing the forum to ask questions about foreign galaxies ... many thanks.

Galaxy Ref: 587742572682084477

Budgieye

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Re: Sunday 22nd April 2012: ancient but still going
« Reply #3 on: April 23, 2012, 05:32:21 am »
I remembered this one SDSS J165401.24+625354.9

Saturday August 7 2010 White dwarf stars are hot, aren't they?

which peaked at 5000 Å

but your new one is even cooler.   :)
« Last Edit: April 23, 2012, 05:35:28 am by Budgieye »

graham d

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Re: Sunday 22nd April 2012: ancient but still going
« Reply #4 on: April 23, 2012, 09:15:31 am »
Excellent Alice :)
To get a feel for blackbody spectra go to
http://phet.colorado.edu/sims/blackbody-spectrum/blackbody-spectrum_en.html
click run
Zoom in on the wavelength scale- to 0.75 micrometres; that's 7500 angstrom
Zoom the intensity scale a couple of clicks
toggle temperature from say 3700 K to 4100K as they report and adjust the intensity to keep the temperature within bounds

When I peruse the sdss spectrum, and sdss keeps the continuum, for me it peaks around about 7800 Angstrom on the scale to 1.5 micrometres
and the temperature appears closer to 3700K than 4100K. The authors will add a few corrections but the applet for a perfect black body is a great learning tool. There is also an sdss tutorial I read a few years ago.

Try it for the Sun and note the number of clicks needed on the intensity to scale it.

Why not try it for the lower limit 300K; ca. room temperature (300K-273K(O celsius) =27 Celsius; scale down to e-12

The radiation intensity is proportional to Temperature to the 4th power so click many many  times to get the red line

Imagine going down to 2.736 K!; the radiation intensity is tiny. Infact, I've never been able to find an applet that scales down this far. If anyone wants to modify a program please do.
« Last Edit: April 23, 2012, 09:31:39 am by graham d »