How Much Mass Makes a Black Hole? Astronomers Challenge Current Theories

Aug 18, 2010
This artist’s impression shows the magnetar in the very rich and young star cluster Westerlund 1. This remarkable cluster contains hundreds of very massive stars, some shining with a brilliance of almost one million suns. European astronomers have for the first time demonstrated that this magnetar — an unusual type of neutron star with an extremely strong magnetic field — was formed from a star with at least 40 times as much mass as the Sun. The result presents great challenges to current theories of how stars evolve, as a star as massive as this was expected to become a black hole, not a magnetar.

(PhysOrg.com) -- Using ESO's Very Large Telescope, European astronomers have for the first time demonstrated that a magnetar -- an unusual type of neutron star -- was formed from a star with at least 40 times as much mass as the Sun. The result presents great challenges to current theories of how stars evolve, as a star as massive as this was expected to become a black hole, not a magnetar. This now raises a fundamental question: just how massive does a star really have to be to become a black hole?

To reach their conclusions, the astronomers looked in detail at the extraordinary Westerlund 1, located 16 000 light-years away in the southern constellation of Ara (the Altar). From previous studies, the astronomers knew that Westerlund 1 was the closest super star cluster known, containing hundreds of very , some shining with a brilliance of almost one million suns and some two thousand times the diameter of the Sun (as large as the orbit of Saturn).

The open cluster Westerlund 1 was discovered in 1961 from Australia by Swedish astronomer Bengt Westerlund. This cluster is behind a huge of gas and dust, which blocks most of its visible light. The dimming factor is more than 100 000, and this is why it has taken so long to uncover the true nature of this particular cluster.

This image of the young star cluster Westerlund 1 was taken with the Wide Field Imager on the MPG/ESO 2.2-metre telescope at ESO’s La Silla Observatory in Chile. This remarkable cluster contains hundreds of very massive stars, some shining with a brilliance of almost one million suns. Although most stars in the cluster are hot blue supergiants, they appear reddish in this image as they are seen through interstellar dust and gas. European astronomers have for the first time demonstrated that the magnetar — an unusual type of neutron star with an extremely strong magnetic field — that lies in the cluster was formed from a star with at least 40 times as much mass as the Sun. The result presents great challenges to current theories of how stars evolve, as a star as massive as this was expected to become a black hole, not a magnetar.

Westerlund 1 is a unique natural laboratory for the study of extreme stellar physics, helping astronomers to find out how the most massive stars in our Milky Way live and die. From their observations, the astronomers conclude that this extreme cluster most probably contains no less than 100 000 times the mass of the Sun, and all of its stars are located within a region less than 6 light-years across. Westerlund 1 thus appears to be the most massive compact young cluster yet identified in the Milky Way galaxy. All stars so far analysed in Westerlund 1 have masses at least 30-40 times that of the Sun. Because such stars have a rather short life -- astronomically speaking -- Westerlund 1 must be very young. The astronomers determine an age somewhere between 3.5 and 5 million years. So, Westerlund 1 is clearly a “newborn” cluster in our galaxy.

“If the Sun were located at the heart of this remarkable cluster, our night sky would be full of hundreds of stars as bright as the full Moon,” says Ben Ritchie, lead author of the paper reporting these results.

Westerlund 1 is a fantastic stellar zoo, with a diverse and exotic population of stars. The stars in the cluster share one thing: they all have the same age, estimated at between 3.5 and 5 million years, as the cluster was formed in a single star-formation event.

A magnetar is a type of neutron star with an incredibly strong magnetic field -- a million billion times stronger than that of the Earth, which is formed when certain stars undergo supernova explosions. The Westerlund 1 cluster hosts one of the few magnetars known in the . Thanks to its home in the cluster, the astronomers were able to make the remarkable deduction that this magnetar must have formed from a star at least 40 times as massive as the Sun.

As all the stars in Westerlund 1 have the same age, the star that exploded and left a magnetar remnant must have had a shorter life than the surviving stars in the cluster. “Because the lifespan of a star is directly linked to its mass -- the heavier a star, the shorter its life -- if we can measure the mass of any one surviving star, we know for sure that the shorter-lived star that became the magnetar must have been even more massive,” says co-author and team leader Simon Clark. “This is of great significance since there is no accepted theory for how such extremely magnetic objects are formed.”

The astronomers therefore studied the stars that belong to the eclipsing double system W13 in Westerlund 1 using the fact that, in such a system, masses can be directly determined from the motions of the stars.

This video is not supported by your browser at this time.
In this video we fly through the young star cluster Westerlund 1 and close in on the strange magnetar that lies within it. This remarkable cluster contains hundreds of very massive stars, some shining with a brilliance of almost one million suns. European astronomers have for the first time demonstrated that the magnetar — an unusual type of neutron star with an extremely strong magnetic field — was formed from a star with at least 40 times as much mass as the Sun.

By comparison with these stars, they found that the star that became the magnetar must have been at least 40 times the mass of the Sun. This proves for the first time that magnetars can evolve from stars so massive we would normally expect them to form black holes. The previous assumption was that stars with initial masses between about 10 and 25 solar masses would form neutron stars and those above 25 solar masses would produce .

“These stars must get rid of more than nine tenths of their mass before exploding as a supernova, or they would otherwise have created a black hole instead,” says co-author Ignacio Negueruela. “Such huge mass losses before the explosion present great challenges to current theories of stellar evolution.”

“This therefore raises the thorny question of just how massive a star has to be to collapse to form a black hole if stars over 40 times as heavy as our Sun cannot manage this feat,” concludes co-author Norbert Langer.

The formation mechanism preferred by the astronomers postulates that the star that became the magnetar -- the progenitor -- was born with a stellar companion. As both stars evolved they would begin to interact, with energy derived from their orbital motion expended in ejecting the requisite huge quantities of mass from the progenitor star. While no such companion is currently visible at the site of the magnetar, this could be because the supernova that formed the caused the binary to break apart, ejecting both stars at high velocity from the cluster.

“If this is the case it suggests that binary systems may play a key role in stellar evolution by driving mass loss — the ultimate cosmic ‘diet plan’ for heavyweight stars, which shifts over 95% of their initial mass,” concludes Clark.

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More information: The research will soon appear in the research journal Astronomy and Astrophysics (“A VLT/FLAMES survey for massive binaries in Westerlund 1: II. Dynamical constraints on magnetar progenitor masses from the eclipsing binary W13”, by B. Ritchie et al.). The same team published a first study of this object in 2006 (“A Neutron Star with a Massive Progenitor in Westerlund 1”, by M.P. Muno et al., Astrophysical Journal, 636, L41).

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User comments : 31

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frajo
3.9 / 5 (7) Aug 18, 2010
From finiter's link:
THE ULTIMATE THEORY IN PHYSICS
...
The new theory can resolve all the existing problems in present day physics.
Life is too short to read everything. I'm grateful for hints like these that help me not to waste my time.
GSwift7
5 / 5 (3) Aug 18, 2010
Hmmm. When I see something that doesn't look right, I usually go back and make sure I'm seeing it correctly. There are several things here that have been inferred or derived by theory rather than direct observation. I wouldn't run out and burn my cosmology books just yet. When you find just one example in the entire visible sky of this type of object, you need to consider the posibility that your observations aren't what they seem, or that one or more of your assumptions are wrong. Occam's razor, Occam's razor, repeat after me.
gunslingor1
5 / 5 (2) Aug 18, 2010
They explain what they THINK forms a neutron star and a black whole. But I haven't ever heard what forms a magnitar? Anyone know?

Is it possible that the spin of the progenator affects what forms?

Is it possible that the magnitar formed, then gobbled up a companion star to reach the current mass?

What is the fate of a magnitar star?

zevkirsh
1 / 5 (1) Aug 18, 2010
magnetar the movie is going to be a blockbuster.
Xaero
1 / 5 (7) Aug 18, 2010
Actually we can find many articles about magnetic field of black holes - so what is so surprising, if we find some? For example, recently we discussed, how magnetic field drags the matter into black holes from distance in connection to LHC risk of black holes formation....

http://www.space....tic.html
fmfbrestel
5 / 5 (4) Aug 18, 2010
http://en.wikiped...Magnetar

There you go gunslingor. Very well referenced article.
Baseline
2 / 5 (7) Aug 18, 2010
Yet another piece of evidence that the standard solar model is woefully inadequate when it comes to matching observations. As an added bonus the theory for black hole formation takes another hit as well. The evidence is beginning to pile up suggesting that we aren't dealing with giant balls of gas.
MarkyMark
5 / 5 (1) Aug 19, 2010
The evidence is beginning to pile up suggesting that we aren't dealing with giant balls of gas.


And what exactly are they made up of then?
GSwift7
4.5 / 5 (4) Aug 20, 2010
Oh come on. Giant balls of gas? That's right, they are not giant balls of gas. The matter in a compact object like a neutron star, magnetar, or black hole is not in gas phase. Conditions in these bodies make it a certainty that the matter cannot remain in gas form. It is extremely unlikely that any whole atoms remain intact under those conditions, at least not as stable entities. The only way to pack that much stuff into such small volume would involve tight packing of something we probably haven't seen yet. Whatever makes up the sub-atomic particles we are aware of, for example. It's probably a falacy to even think of what lies inside those bodies as matter. It's more likely something we would not recognize as matter, as we define matter.
yyz
3.4 / 5 (5) Aug 20, 2010
"It's probably a falacy to even think of what lies inside those bodies as matter. It's more likely something we would not recognize as matter, as we define matter."

Degenerate matter: http://en.wikiped...e_matter
Xaero
1.5 / 5 (6) Aug 21, 2010
By relativity black holes are formed by vacuum and they're contain a gravitational singularity inside.
Xaero
1 / 5 (7) Aug 21, 2010
..from which it's evident, black hole with magnetic field is impossible.
yyz
4.2 / 5 (5) Aug 21, 2010
"..from which it's evident, black hole with magnetic field is impossible."

One of your favorite 'peer reviewed' sites says otherwise: http://www.newsci...6535.000

If AWT predicts no magnetic fields, what may account for these observations. What does google say?

Xaero
Aug 21, 2010
This comment has been removed by a moderator.
Skeptic_Heretic
4 / 5 (4) Aug 21, 2010
By relativity black holes are formed by vacuum and they're contain a gravitational singularity inside.

No, that is not what relativity says.
Xaero
1 / 5 (5) Aug 21, 2010
Yes kid, this is exactly what the relativity says. Learn the relativity first before trolling at public.

"A black hole, according to the general theory of relativity, is a region of space from which nothing, including light, can escape."

http://en.wikiped...ack_hole

"At the center of a black hole as described by general relativity lies a gravitational singularity, a region where the spacetime curvature becomes infinite.."
Skeptic_Heretic
4.3 / 5 (6) Aug 21, 2010
Yes kid, this is exactly what the relativity says. Learn the relativity first before trolling at public.

"A black hole, according to the general theory of relativity, is a region of space from which nothing, including light, can escape."

http://en.wikiped...ack_hole

"At the center of a black hole as described by general relativity lies a gravitational singularity, a region where the spacetime curvature becomes infinite.."

Black holes are not created by vaccuum as you've asserted.
Xaero
1 / 5 (5) Aug 21, 2010
They're formed with region of space, i.e. vacuum.
Skeptic_Heretic
4 / 5 (4) Aug 21, 2010
They're formed with region of space, i.e. vacuum.

Space is not a vaccuum.
Xaero
1 / 5 (4) Aug 21, 2010
This indeed makes a big difference...;-) Well, by relativity black hole is pin-point singularity surrounded with space. Apparently unphysical stuff.
Skeptic_Heretic
4 / 5 (4) Aug 21, 2010
This indeed makes a big difference...;-) Well, by relativity black hole is pin-point singularity surrounded with space. Apparently unphysical stuff.
Relativity states that space-time is physical. You don't appear to understand relativity. I can teach you if you want to learn.
Xaero
1 / 5 (4) Aug 21, 2010
..relativity states that space-time is physical.
It maybe - but now we are talking about singularities and black holes, not just about some space-time. If you want teach me the general relativity... - do you know, what is unphysical on concept of black holes and Schwarzschild's solution (which Einstein opposed so obstinately, BTW)?
Husky
5 / 5 (2) Aug 21, 2010
i would think the huge magnetic field provides some resistance to compression by gravity, also the inertia of very fast spinning matter would offer resistance to moving inward? Since magnetars are known to gradually lose their magnetic field through soft gamma ray emissions it would be interesting to observe a huge > 25 solarmass magnetar losing its field below a possibly critical threshold and whether this allows a postponed formation of a black hole to take effect
Xaero
1 / 5 (5) Aug 22, 2010
Einstein himself thought that black holes would not form, because he held that the angular momentum of collapsing particles would stabilize their motion at some radius. This led the general relativity community to dismiss all results to the contrary for many years.

http://jstor.org/.../1968902

Funny thing is, mainstream media are still claiming, it was just an Einstein, who turned black hole concept into life, for example here:

http://www.telegr...sts.html
Skeptic_Heretic
5 / 5 (2) Aug 22, 2010
- do you know, what is unphysical on concept of black holes and Schwarzschild's solution (which Einstein opposed so obstinately, BTW)?

Well yes, it's the fact there's more than one solution for angular deflection. This was due to the fudge factor that Einstein included in his original version of relativity to produce a static space-time. He was vehemently opposed to the expansion principle, until he found that the expansion principle was correct.

It was what he referred to as his greatest blunder, but this isn't "unphysical" unless you ignore QED.
Xaero
1 / 5 (5) Aug 22, 2010
Do you know, what is unphysical on concept of black holes and Schwarzschild's solution (which Einstein opposed so obstinately, BTW)?

Einstein stance to statical Universe concept has nothing to do with the above question. Angular deflection (...of what?) the more.
Skeptic_Heretic
5 / 5 (2) Aug 22, 2010
Einstein stance to statical Universe concept has nothing to do with the above question. Angular deflection (...of what?) the more.
Of light. Are you trying to construct a trap question? If so, you're doing so rather obviously, and you're not so good at it.
Xaero
1 / 5 (5) Aug 22, 2010
For silly people nearly every question appears trapping. Do you know, why Einstein objected Schwarzschild's model? Do you know, what is really wrong with it?

If you don't know about it, it's not shame to admit it - only a few people on the world know the answer, after all. The silly stance is to pretend, you know the answer, instead.
Aranoff
4.7 / 5 (3) Aug 22, 2010
When physicists say a black hole, BH, is an object from which nothing can escape, they make me angry, for this displays their ignorance of physics! Time on earth is slower than time on a satellite due to the mass of the earth. This is critical for GPS. A larger mass would have a larger slowing of time. For a large enough mass, time would stop. A BH is a huge mass such that time stops at the surface, called the Event Horizon. Since nothing can reach the EV, please do not say nothing can get out!

What happens when things fall into a BH is that they speed up due to conservation of angular momentum. Part falls to the EV, and part escapes. The conversation of mass into energy is 50%. Contrast this with a hydrogen bomb, where the conversation of mass into energy is 0.1%.

The huge energy leaving the vicinity of the BH clears out the region nearby. Eventually a BH reaches a maximum size, where there is nothing in the region to fall into.
Xaero
1 / 5 (5) Aug 22, 2010
When physicists say a black hole, BH, is an object from which nothing can escape, they make me angry, for this displays their ignorance of physics!
Actually, if black hole can lose its energy via gamma rays because of its magnetic field (as Husky have said) - it can evaporate its mass a much faster radiative way, then the Hawking mechanism considers.
Skeptic_Heretic
3 / 5 (2) Aug 22, 2010
When physicists say a black hole, BH, is an object from which nothing can escape, they make me angry, for this displays their ignorance of physics!
Actually, if black hole can lose its energy via gamma rays because of its magnetic field (as Husky have said) - it can evaporate its mass a much faster radiative way, then the Hawking mechanism considers.

Explain that mechanism and collect your Nodel prize.
Xaero
1 / 5 (4) Aug 22, 2010
Too late, this theory was formulated by Robert Duncan and Christopher Thompson in 1992 already...