Spectacular Hypergiant Star Found Passing Through "Forbidden Zone"
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December 10, 2012

Spectacular Hypergiant Star Found Passing Through "Forbidden Zone"

 

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A European research team has discovered an extraordinary hypergiant star as it went through while it went through an extremely rare stage called the 'Yellow Evolutionary Void'. The team have found that the surface temperature of the super-luminous star HR 8752 increased by about 3000 degrees in less than three decades. The discovery marks an important step closer to unravelling the evolution of the most massive stars. The discovery is an important step forward to resolve the enigma of the hypergiants, the most luminous and massive stars of the Galaxy. Hypergiants can shine millions of times brighter than the Sun, and they often have a diameter several hundred times greater.

The astronomers investigated the hypergiant star HR 8752 for 30 years while it traversed the 'Yellow Evolutionary Void' --a short stage in the lives of the most massive stars when they become very unstable. The team finds that the surface temperature of HR 8752 rose surprisingly fast from 5000 to 8000 degrees in less than 30 years.

HR 8752 is a quarter million times more luminous than the Sun. The powerhouse is therefore visible with normal binoculars at large distance from the Earth in the Northern constellation of Cassiopeia. There are currently only 12 hypergiants known in our Galaxy.

The 'Yellow Evolutionary Void' is a unique stage in the short life of a hypergiant when its temperature and luminosity can quickly change. The team has discovered that the atmospheres are very unstable inside the Void because outwardly directed forces act equal or sometimes even stronger than the force of gravity. Due to the unstable atmosphere, hypergiants lose tremendous weight in this 'forbidden zone', which can sometimes amount to the mass of the Sun in a year.

When a hypergiant enters the 'Evolutionary Void' the star tries to it leave as quickly as possible. That is why almost all hypergiants are found outside the Void.The team finds that HR 8752 is a very rare hypergiant which has partly traversed the Void. The changes of its atmosphere were closely monitored with regular observations over 30 years.

Alex Lobel, co-author of the study and ROB scientist explains that "HR 8752 was around 1980 identical to the eruptive hypergiant Rho Cas of spectral type F, but then the temperature of HR 8752's atmosphere rapidly increased by 3000 degrees and now shows the spectral properties of a hotter A-type star. We are baffled about the tremendous changes of HR 8752 in that period of time."

Between 1900 and 1980 the atmospheric temperature of HR 8752 stayed almost constant around 5000 degrees, but it rose very rapidly to 8000 degrees between 1985 and 2005. The team calculates that the stellar radius decreased from 750 to 400 times that of the Sun. In 1985 the team embarked on a long-term spectroscopic observing program when it found that the remarkable hypergiant was exactly at the border of the 'Yellow Void' and started to cross over.

"HR 8752 had to struggle through the Void which has changed the physical properties of its atmosphere", Lobel adds. The team further demonstrates that the Void actually consists of two parts in which the atmosphere of the hypergiant is unstable. They result from ionization of large amounts of hydrogen and helium gas in the atmosphere, divided by a small zone around 8000 degrees where it becomes more stable.

The fate of HR 8752 is currently unclear but there are strong hints that these massive hypergiants may perish in a powerful supernova explosion. Or they quickly traverse the Void and transform into a hotter type of erratic stars known as the "Luminous Blue Variables".

In either case that will not pass unnoticed according to Kees de Jager and Hans Nieuwenhuijzen, the astronomers of the Netherlands Institute for Space Research in Utrecht who directed the research of HR 8752 over the past three decades. The discovery is an important new step for explaining the existence of these extreme stars. A number of other hypergiants with similar spectacular properties is expected to exist in the Milky Way. The search for these remarkable stars with dramatic changes over human timescales has just begun, but has been forever put on track.

The image below is an artist's rendition of the hypergiant HR 8752 traversing the 'Yellow Evolutionary Void'. The graph plots the temperature at the surface of the star observed over a century. It rose from 5000 to 8000 degrees between 1985 and 2005, while the radius of the hypergiant decreased from 750 to 400 times the radius of the Sun.

For more information: Arxiv pre-print: dx.doi.org/10.1051/0004-6361/201117166 Journal reference: Astronomy and Astrophysics.

 

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The Daily Galaxy via the Royal Observatory of Belgium

Image credit: © A. Lobel, Royal Observatory of Belgium

Comments

Ooohh, Just wanted to respond. I thoroughly loved your post. Keep up the great work. :)

What I don't understand; due to ignorance, if there is a black hole at the center of the
Milky Way and nothing can escape from it, not even light. Then, why is it glowing? If light
can't escape from it, the center of the galaxy should be dark, not lit up like a X-mas tree. It
has to be a super sun, like this one. Not a black hole. Astronuts are dead wrong, on this one.

“The team has discovered that the atmospheres are very unstable inside the Void because outwardly directed forces act equal or sometimes even stronger than the force of gravity”.

AD: The question is then: How can the formation processes in a supposedly “hyper massive star” overcome the force of “gravity”?

And the answer is: Strong electromagnetism working in circuits. "The Yellow Evolutionary Void" is just a momentary extra charge in the formation process, gained from outside electric forces of the star.

The formation process has nothing to do with the ancient (and contradicted) idea of “gravity”.

The bound of light can escape is event horizon. If any reaction occurs beyond this limit, we can't see anything. But if reactions occurs out of this limit, we can see the effects. For example they devour other stars or masses of galactic core materials etc. So, we can see the events on cover of a black hole.

And one thing more, black holes can radiate. Because they can wave null energy level by emitting gravitational forces. And if this situation occurs, some particles can appear in empty space by couples matter and anti matter. If this occurs exactly on the event horizon and the inner particle is an anti matter, the blackhole loses its mass. And other part emits. So, even if there is no mass around the black hole, we can see the energy or matterial flow from it.

@Cybermilitia,
You wrote: "So, even if there is no mass around the black hole, we can see the energy or matterial flow from it".
AD: The only way scientist can observe a so called "black hole" is by the movement of gasses and particles around it.

So per definition there is always mass around the hypothetic black hole.

The question is then: How can a "black hole" decide what to pull inwards and what to push outwards?

Not only way. Mass bends the space-time. So, this means normally direct way of light bends. If you have a light source behind the black hole, you can observe the bended space-time and red-shift. Redshift is a phenomenon related to the light's frequency. It's about Doppler effect or mass effect. You can see observe this phenomenon as a gravity effect or the effect of the expansion of the universe. So you can notice a black hole with this way as well.

The answer of your question: Blackholes can not decide it. It must be a statistical event. Just chance. Hawking used this reason to prevent from contravention of 2nd Principle of Thermodynamics. 2nd principle says the total entropy can not decrease as time goes by. But everything that has entropy must radiate. Actually, there is nothing has not entropy in the universe. It's related to time flow direction. We can go only forward in time, because total entropy must increase. Anyway, if blackholes can not radiate, they don't have entropy. So, if you put a mass has normally entropy into the black hole, you can decrease total entropy. And it's illegal.

What regulates the amount of matter entering a black hole and if to much, then
will it close down or choke?


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