Disruption of giant molecular clouds by massive star clusters

Jun 02, 2011

(PhysOrg.com) -- New computer simulations show that the light from massive stars is, by itself, enough to blow apart the nebula where the stars are born. While this 'radiation pressure' was by and large overlooked in the past, these new results show how, even before a single star explodes as a supernova, massive stars carve out huge bubbles and limit the star formation rates in galaxies.

The findings are being presented by Dr. Elizabeth Harper-Clark and Prof. Norman Murray of the Canadian Institute for Theoretical Astrophysics (CITA) at the 2011 meeting of the Canadian Astronomical Society (CASCA) in London, ON, Canada.

Galaxies are the birthplace of . As the stellar population changes, so the galaxy evolves. Yet, the stately pace of this evolution remains unexplained. It is generally believed that the pace of is regulated by the outflow of energy from other stars and possibly .

The lifetime of a Giant Molecular Cloud (GMC, a large star-forming nebula) and the total mass of stars that form within it are crucial to the understanding of star formation rates across a galaxy. In particular, the stars within a GMC can disrupt their host and consequently quench further star formation. Indeed, observations show that our own galaxy, the Milky Way, contains GMCs with extensive expanding bubbles but without , indicating that the GMCs are being disrupted before any occur.

Radiation from stars interacts with the gas in the surrounding GMC in two main ways: ionization and radiation pressure. works by forcibly ejecting electrons from atoms at high speed; these electrons then heat up the gas, increasing the gas pressure. Radiation pressure is more subtle and often ignored -- the momentum from the light is transferred to the when light is absorbed. These momentum transfers add up, always pushing away from the light source, and produce the most significant effect, according to these simulations.

The simulations performed by Harper-Clark represent the first calculations of the effects of on GMCs and show that this pressure is capable of disrupting such clouds, the main star-forming units in galaxies. "The results suggest that the slow rate of star formation seen in galaxies across the universe may be the result of radiative feedback from ," says Professor Murray, Director of CITA.

Simulating entire GMCs is challenging, due to the large variety of physics that needs to be included and the computational power required to accurately simulate a GMC over tens of millions of years. Using the radiative-magneto-hydrodynamic code Enzo, Harper-Clark ran multiple simulations of GMCs under different conditions.

Harper-Clark robustly found that with only the light emitted by the stars (radiation) during their lifetimes the GMC could be completely blown apart, cutting off star formation after a percentage between 5% and 20% of the original cloud's mass had been converted into stars.

Interestingly, when supernovae were included in the simulations they were found to be unimportant. Both with and without the light from stars, supernovae were not significant on the disruption of the GMC, nor did they alter the subsequent star formation. With no radiation feedback, supernovae exploded in a dense region leading to rapid cooling. This robbed the supernovae of their most effective form of feedback, hot gas pressure. When radiative feedback is included, the supernovae explode into an already evacuated (and leaky) bubble, allowing the hot gas to expand rapidly and leak away without affecting the remaining dense GMC gas. "These simulations suggest that it is the light from stars that carves out nebulae, rather than the explosions at the end of their lives," says Dr. Harper-Clark.

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Provided by Canadian Astronomical Society

5 /5 (3 votes)

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User comments : 8

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1.4 / 5 (11) Jun 03, 2011

Although this is only "a computer simulation", it may explain how a glowing ball of waste products (photosphere) can accumulate and be suspended above neutron stars to produce ordinary-looking stars like the Sun.

See: "Neutron Repulsion", The
APEIRON Journal, in press, 19 pages (2011)

1.3 / 5 (14) Jun 03, 2011
Galaxies are the birthplace of stars.
What are galaxies if not a collection of a whole lot of stars?
Where does the first stars come from? Are they implying that galaxies appear suddenly in one massive POP, spewing out stars at prodigious rates, before the birth of stars and supernovas can disrupt any further star formation by blowing the gas away? So then they don't really know where stars come from and hence by implication where galaxies come from. This means that the current theories of cosmology and cosmogony are really a lot of hot air as far as explanatory power is concerned. If you cannot explain where stars and galaxies come from or how they are created, you cannot explain anything else.
But of course it doesn't mean they should stop trying, just stop pretending they know it all.
5 / 5 (4) Jun 03, 2011
The article clearly states that 5% to 20% of the GMC mass is converted into stars before the GMC is crippled by radiation. The remaining gass does not dissappear, some of it may condense into new clouds at later stages unless it is blown entirely out of the galaxy by some extreme star burst formation or perhaps an active galactic nucleus.
1 / 5 (4) Jun 04, 2011

See: "Neutron Repulsion", The
APEIRON Journal, in press, 19 pages (2011)


A recent interview with Czech astronomer, Dr. Ivanka Charvátová, confirms: Climate change is caused by changes in solar inertial motion (SIM):



With kind regards,
Oliver K. Manuel

1 / 5 (3) Jun 07, 2011
5 / 5 (2) Jun 08, 2011
Oliver insists on spamming the site with identical posts hear is a copy of my reply.
shows that other scientists also disagree with the global warming story

army of government-paid climatologists
Ivanka Charvátová is government paid.

Gravitational interaction of orbiting planets with the Suns central neutron star

waste products (H/He-rich photosphere
not rated yet Jun 08, 2011
Wolf Minimum (1270-1350) 160 - 170
Spörer Minimum (~1430-1520) 190 - 190
Maunder Minimum (~1620-1710) 170 - 130



Beginnings 520 / 3 = 173


1790 + 179 = 1969 average
1790 + 160 = 1950 shortest beginning to beginning
1790 + 130 = 1920 shortest ending to ending
1790 + 190 = 1980 longest interval of any kind


5 / 5 (1) Jun 08, 2011
And where did this thing come from in the interview?
