Astronomers reveal a rapidly spinning core inside old stars

Dec 08, 2011
Comparison of diameter and rotation rate of a redgiant to the sun. Image Credit: Paul G. Beck, KU. Leuven.

(PhysOrg.com) -- Scientists have made a new discovery about how old stars called 'red giants' rotate, giving an insight into what our sun will look like in five billion years.

An international team of astronomers led by PhD student Paul Beck from Leuven University in Belgium have managed to look deep inside some old stars and discovered that their cores spin at least ten times as fast as their surfaces. The result appeared today in the journal Nature.

It has been known for a long time that the surfaces of these stars spin slowly, taking about a whole year to complete one rotation.  The team has now discovered that the cores at the heart of the stars spin much faster with about one rotation per month. The discovery was made possible because of the ultra high precision of the data from NASA's Kepler space telescope.

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This artist impression illustrates the rotation inside a red giant star. Such stars have radii of more than 5 times the radius of the Sun. Initially the outer layers, which are rotating very slowly, are shown. When these layers are hidden, the hot core of the star, which rotates 10 times faster than the surface, becomes visible. While the surface of this red giant needs about one year to complete a full revolution, it takes the core only a few weeks to rotate once. For better visual effect, the rotation rate is artificially increased. In the animation, 60 seconds correspond to an entire year in real time. Credit: Paul G. Beck, KU. Leuven

Beck and his collaborators analysed travelling through the , which appear at the as rhythmic variations in the stars' brightness. The study of such waves is called asteroseismology, and is able to reveal the conditions deep inside a star which would otherwise remain hidden from view. Different waves probe different parts of the star and by a detailed comparison of the depth to which these waves travel inside the star, the team found evidence of the rotation rate and its dramatic increase towards the stellar . “It is the heart of a star, which determines how it evolves," says Beck, "and understanding how a star rotates deep inside helps us to understand how stars like our Sun will grow old."

The fast rotating core becomes visible, when the convectibe envelope is removed. Image Credit: Paul G. Beck, KU. Leuven.

The stars studied in the article are so-called red giants. Our Sun will become a red giant in about 5 billion years. Their outer layers have expanded to more than 5 times their original size, and cooled down significantly so that they appear red. Meanwhile, their cores did exactly the opposite, and have contracted to an extremely hot and dense environment. To understand what has happened to a star’s spin consider what happens to an ice skater performing a pirouette. A spinning ice skater will slow down if the arms are stretched far out, and will spin faster if the arms are pulled tightly to the body. Similarly, the rotation of the expanding outer layers of the giant has slowed down, while the shrinking core has spun up.

The Kepler space telescope, is one of NASA’s most successful current space missions. Designed to search for Earth-size planets in the habitable zone of distant stars, the mission has detected numerous planetary candidates, and has confirmed many bona fide planets outside our solar system. Kepler is capable of detecting variations in a star’s brightness of only a few parts in a million, and its measurements are therefore ideally suited to detect the tiny waves mentioned above. The effect of rotation on these waves is so small, that its discovery needed two years of almost continuous data gathering by the Kepler satellite.

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More information: Fast core rotation in red-giant stars as revealed by gravity-dominated mixed modes, DOI:10.1038/nature 106212

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User comments : 17

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typicalguy
4.9 / 5 (17) Dec 08, 2011
Oh no...someone is going to show up now...
omatumr
Dec 08, 2011
This comment has been removed by a moderator.
rawa1
1.7 / 5 (6) Dec 08, 2011
This effect has its analogy in dark matter effect of rotational curves of stars at the perimeter of galaxies. Even our Sun has a core, which is rotating faster, than the surface of Sun. It could be the dark matter effect as well.

http://www.wired....tter-sun
http://news.softp...01.shtml

The composition of this dark matter is disputable though. The neutrinos are difficult to consider, because their speed would be a much higher, than the escape velocity of Sun (520 km/sec) at the temperatures existing inside of Sun.
rawa1
3.3 / 5 (4) Dec 08, 2011
Here you can read, it takes more than 12.500 years for photons generated from nuclear reaction at Sun core to reach the solar surface. So we can ask, how much energy and matter in the form of photons is stored beneath the surface of Sun? The Sun is losing about 3.1 x 10^29 grams over the entire life, which is 0.008 percent of its current mass.

http://www.astron...491.html

The contribution of trapped photons to the solar mass is therefore quite negligible, but their radiation pressure hasn't to be quite negligible. The pressure of radiation is behaving like the antigravity force, which not only protects the solar mass before gravitational collapse, but it would keep the particles in mutual repulsion, which could account to the fact, the whole the solar mantle is rotating as a single body.
dtyarbrough
1.5 / 5 (8) Dec 08, 2011
The hot gases at the center are compressed and the cooler gases at the surface expand. Right!! Someone should tell them that heat causes expansion and rises to the surface. Its these convection currents that create the spin. Friction due to spin creates the heat, not nuclear reactions.
omatumr
1.3 / 5 (12) Dec 08, 2011
Fig 2: http://www.omatum...tnuc.pdf

Two forms of one fundamental entity - [a(P )/(e-) pair], [compacted/expanded] or [neutron/H-1 atom] - comprise our entire benevolent universe.

a.) At Z/A = 0, a nucleus of neutrons (N) only has additional stored potential energy, mass (m), from N-N repulsion

b.) At Z/A = 1, a nucleus of protons (P ) only has the same additional stored potential energy from P-P repulsion as N-N repulsion, (m), plus Coulomb repulsion between charges produces additional Coulomb potential energy (Ec). I.e., total additional potential energy is m' = m Ec.

c.) At Z/A = 0.5, a nucleus with equal numbers of neutrons (N) and protons (P ) loses potential energy, rest mass from attractive N-P interactions to produce the stable nuclear species at the cores of ordinary chemical elements.

a.) Compacted: Under high pressure in the cores of atoms, stars and galaxies, the P /e- pair compacts to a neutron (N).

b.) Expanded: Under low pressure,
omatumr
1.3 / 5 (14) Dec 08, 2011
Corrections to replace plus symbol

Two forms of one fundamental entity - [a(Pplus)/(e-) pair], [compacted/expanded] or [neutron/H-1 atom] - comprise our entire benevolent universe.

b.) At Z/A = 1, a nucleus of protons (Pplus) only has the same additional stored potential energy from P-P repulsion as N-N repulsion, (m), plus Coulomb repulsion between plus charges produces additional Coulomb potential energy (Ec). I.e., total additional potential energy is m' = m plus Ec.

c.) At Z/A = 0.5, a nucleus with equal numbers of neutrons (N) and protons (Pplus) loses potential energy, rest mass from attractive N-P interactions to produce the stable nuclear species at the cores of ordinary chemical elements.

a.) Compacted: Under high pressure in the cores of atoms, stars and galaxies, the Pplus/e- pair compacts to a neutron (N).

b.) Expanded: Under low pressure, (to be continued) . . .
that_guy
2.3 / 5 (3) Dec 08, 2011
If a fat man spins, you can readily tell that his core spins faster than his outer layers of fat - The fat would fall behind if his skin didn't force it to keep up.

A fat planet, like saturn, spinds faster at the core than its outer surface.

and a fat star...

@typical guy...you got that one right on the nose.

Pirouette
3.4 / 5 (5) Dec 08, 2011
Oh no...someone is going to show up now...


LOL. . .typicalguy once again proves his developing talent of ESP.
Pirouette
1.6 / 5 (7) Dec 08, 2011
Oh no...someone is going to show up now...


Speaking of showing up: http://www.physor...lem.html

Frank$hithead showed up and was unable to provide his own observation regarding the question of the article.
jsdarkdestruction
5 / 5 (2) Dec 09, 2011
Oh no...someone is going to show up now...


Speaking of showing up: http://www.physor...lem.html

Frank$hithead showed up and was unable to provide his own observation regarding the question of the article.

you are just making yourself look bad, it would be wise to stop.
Parsec
1 / 5 (1) Dec 09, 2011
The hot gases at the center are compressed and the cooler gases at the surface expand. Right!! Someone should tell them that heat causes expansion and rises to the surface. Its these convection currents that create the spin. Friction due to spin creates the heat, not nuclear reactions.

Solar energy isn't created by nuclear reactions? It's caused by friction? my suggestion to you... stay off the pipe at least a few hours before posting. It will help you a lot.
FrankHerbert
1.8 / 5 (66) Dec 09, 2011
What an ironic comment coming from Omatumr.
omatumr, Member since: September 24, 2007, 11:57 am

Parsec, Member since: September 24, 2007, 11:58 am
FrankHerbert
2.7 / 5 (91) Dec 09, 2011
Well I think we may have figured out who orac is.
jsdarkdestruction
5 / 5 (28) Dec 09, 2011
frankherbert, i find it very unlikely omatumr is parsec, if you look through past posts and such of the 2 imo it becomes pretty clear its 2 different people. like barakan also pointed out something like 50 other people joined on the same day as parsec and omatumr
rawa1
1 / 5 (2) Dec 09, 2011
Well I think we may have figured out who orac is.
I can agree with it, because I was started downvoted with orac just at the moment, when I first objected ommatur's massive spamming in this forum. This doesn't mean, you're not doing the very same with respect to other readers, so you're recognized mass spammer as well.
http://www.aether...bert.gif
jsdarkdestruction
5 / 5 (1) Dec 10, 2011
no, orac is not omatumr either. if you message orac he will respond and he is not oliver, im sure of it.
Anda
not rated yet Dec 12, 2011
That was really funny...
Rawa1 talking about "massive spamming in this forum" :)