Hypergiant star turns out to be 'missing link' after 30 years

Nov 05, 2012
Artist's rendition of the hypergiant HR 8752 traversing the Yellow Evolutionary Void. The graph plots the star's surface temperature (log Teff) observed over a century. It increased from ~5000 to ~8000 C between 1985 and 2005, while the hypergiant's radius decreased from 750 to 400 times the radius of the Sun. Credit: A. Lobel ROB

(Phys.org)—A team of scientists from six European countries reported today they have finalized a thirty years long investigation of a hypergiant star that crossed the Yellow Evolutionary Void. In that period the star's surface temperature quickly rose from five to eight thousand degrees. With this discovery a crucial 'missing link' in the evolution of hypergiant stars has been found. 

The hypergiants are the most currently known in the Universe. The particular star they investigated for thirty years is called HR 8752 and can be observed with in the Northern constellation of . HR 8752 is about 250 thousand times as luminous as our Sun. The Yellow Evolutionary Void is the surface temperature range from about five to twelve thousand degrees. It appears that this range is void of hypergiants, while one would expect in that temperature range at least a few hypergiants slowly heating up during the late part of their evolution.

The team of found that the of hypergiants are unstable inside the Evolutionary Void because the outward directed forces in their atmospheres equalize or become even stronger than the inward . The instability of their atmospheres causes the gargantuan stars to lose tremendous amounts of mass and to traverse the Void in a cosmologically very short timespan. The team has discovered that the Void actually consists of two areas where the atmosphere of hypergiants become unstable, associated with the of hydrogen and respectively, with a narrow stability strip around eight thousand degrees where the atmospheres are slightly more stable.

Three decades

While an analysis of earlier photometric observations showed that, at least from ~1900  to ~1980, HR 8752 stayed at a nearly constant surface temperature of five thousand degrees, the team had some indications that around 1985 this remarkable star was fairly close to or even beyond the low-temperature boundary of the Void. Wondering what would happen, the scientists decided to embark on a long and systematic program of spectroscopic observations that lasted for three decades. These have now shown that in the twenty years period from 1985 to 2005 the star's surface temperature quickly rose from five to eight thousand degrees, while going through a series of events with very strong loss of mass. During the twenty years the radius of HR 8752 has shrunk from 750 to 400 times the radius of the Sun.

Hans Nieuwenhuijzen, former SRON researcher: "Our team made a tremendous effort to combine these observations of HR 8752 and we are delighted to see this marvellous result after so many years. We knew this was the hypergiant to watch and it payed off".

Publication

The observations show the hypergiant star to traverse (part of) the Yellow Evolutionary Void. "They are in fact strong confirmation of the theoretical research on the area of the Void" said team member and former SRON director prof. Kees de Jager, an eminent researcher of the hypergiants. The team published the results last week in Astronomy and Astrophysics, entitled The hypergiant HR 8752 evolving through the Yellow Evolutionary Void.

The team is stepping up new research on hypergiants with the new findings on HR 8752. Other hypergiants may reveal similar spectacular properties with large changes in surface temperature on human time-scales. A number of candidate stars was selected for spectroscopic monitoring and the search for these unusually large temperature changes is on.

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User comments : 8

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Shinichi D_
4.2 / 5 (6) Nov 05, 2012
Kevin? yoooohooooo.. Keeeeevin, where are you?
Torbjorn_Larsson_OM
4.7 / 5 (3) Nov 06, 2012
You are kidding. He (less likely a she) probably didn't even know there was a problem (I didn't). He hasn't any factual science knowledge and, as we can see, not even a superficial familiarity with the issues.
jsdarkdestruction
4.3 / 5 (3) Nov 06, 2012
but the title features the phrase missing link torbjorn. that is like honey to creationists and you will regulalry see kevin jump at his chance to go on a rant about evolution in an unrelated article. or his rants about no one seeing a star born in person....
Shootist
3 / 5 (2) Nov 10, 2012
Might I add that Oliver Manuel hasn't posted since December 29, 2011?

yyz
1 / 5 (1) Nov 10, 2012
"Might I add that Oliver Manuel hasn't posted since December 29, 2011?"

Yeah, but he's still keeping on keeping on with Neutron Nellie etc: https://omanuel.wordpress.com/
Widdekind
1 / 5 (1) Nov 27, 2012
"between 1985 and 2005, the surface temperature of the star had risen rapidly from 5000 to 8000 degrees [and] the radius of the star had decreased from 750 times that of the Sun ... to a mere 400 times the solar radius in 2005"

Inexpertly, the large amount of mass lost during this contraction seemingly "must" have been blown off, in a major mass ejection, of outer atmospheric envelope layers, exposing hotter deeper layers. That would simultaneously explain the decrease in size, and the increase in temperature.
Widdekind
1 / 5 (1) Nov 27, 2012
So, the star has contracted from 800-400 solar radii, and heated from 5000-8000K. Inexpertly, the large amount of mass lost during this contraction seemingly "must" have been blown off, in a major mass ejection, of outer atmospheric envelope layers, exposing hotter deeper layers. That would simultaneously explain the decrease in size, and the increase in temperature.

Red supergiants, to the "right" of the Yellow Evolutionary Void (YEV), on the HR diagram, are enormous. Stars like Betelgeuse & VY Canis Majoris are several thousand Kelvin, and ~10AU across. Thus, they resemble proto-stellar cloud clumps, collapsing onto Hayashi tracks, in the URC of the HR diagram. Supergiant stars seemingly resemble puffed up "Planetary Nebula in the making" -- when they finally eject outer layers, they rapidly expose their smaller bluer cores (so swiftly swinging thru the YEV), similar to WDs becoming exposed at the centers of PNe
Widdekind
1 / 5 (1) Nov 29, 2012
As seen in the following figure, solar-mass stars eventually swell up to >1AU in size, similar to the sizes of red supergiants, like Betelgeuse. Then, cosmically quickly, over ~10Kyr, they gradually blow off their outer layers, producing PNe, whilst increasingly exposing their cores, which then become WDs:

http://chandra.ha...rack.jpg

Inexpertly, there seems to be a connection, between the YEV; and the "Instability Strip" for variable stars. In all cases, some instability occurs, at "yellow" temperatures (~6000K), presumably relating to opacity -- temperature rises, ionization (of Helium?) increases, opacity increases, and building radiation pressure blows away the now-opaque outer layers? If so, then the "Instability Strip" extends all the way to the top of the HRD, and includes not only both types of Cepheids; but also supergiants in the YEV