Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Solving a 30-year-old problem in massive star formation

28.01.2014
An international group of astrophysicists has found evidence strongly supporting a solution to a long-standing puzzle about the birth of some of the most massive stars in the universe.

Young massive stars, which have more than 10 times the mass of the Sun, shine brightly in the ultraviolet, heating the gas around them, and it has long been a mystery why the hot gas doesn't explode outwards.


This false-color Very Large Array image of the ionized gas in the star forming region Sgr B2 Main was used to detect small but significant changes in brightness of several of the sources. The spots and filaments in this image are regions of ionized gas around massive stars. The changes in brightness detected support a model that could solve a 30-year-old question in high mass star formation.

Credit: NRAO/Agnes Scott College

Now, observations made by a team of researchers using the Jansky Very Large Array (VLA), a radio astronomy observatory in New Mexico, have confirmed predications that as the gas cloud collapses, it forms dense filamentary structures that absorb the star's ultraviolet radiation when it passes through them. As a result, the surrounding heated nebula flickers like a candle.

The findings, made by scientists working at Agnes Scott College, Universität Zürich, the American Museum of Natural History, Harvard-Smithsonian Center for Astrophysics, National Radio Astronomy Observatory, European Southern Observatory, and Universität Heidelberg, were published recently in The Astrophysical Journal Letters.

"Massive stars dominate the lives of their host galaxies through their ionizing radiation and supernova explosions," said Mordecai-Mark Mac Low, a curator in the American Museum of Natural History's Department of Astrophysics and an author on the paper. "All the elements heavier than iron were formed in the supernova explosions occurring at the ends of their lives, so without them, life on Earth would be very different."

Stars form when huge clouds of gas collapse. Once the density and temperature are high enough, hydrogen fuses into helium, and the star starts shining. The most massive stars, though, begin to shine while the clouds are still collapsing. Their ultraviolet light ionizes the surrounding gas, forming a nebula with a temperature of 10,000 degrees Celsius. Simple models suggest that at this stage, the gas around massive stars will quickly expand. But observations from the VLA radio observatory show something different: a large number of regions of ionized hydrogen (so-called HII regions) that are very small.

"In the old theoretical model, a high-mass star forms and the HII region lights up and begins to expand. Everything was neat and tidy," said lead author Chris De Pree, a professor of astronomy and director of the Bradley Observatory at Agnes Scott College. "But the group of theorists I am working with were running numerical models that showed accretion was continuing during star formation, and that material was continuing to fall in toward the star after the HII region had formed."

Recent modeling has shown that this is because the interstellar gas around massive stars does not fall evenly onto the star but instead forms filamentary concentrations because the amount of gas is so great that gravity causes it to collapse locally. The local areas of collapse form spiral filaments. When the massive star passes through the filaments, they absorb its ultraviolet radiation, shielding the surrounding gas. This shielding explains not only how the gas can continue falling in, but why the ionized nebulae observed with the VLA are so small: the nebulae shrink when they are no longer ionized, so that over thousands of years, they appear to flicker like a candle.

"These transitions from rarefied to dense gas and back again occur quickly compared to most astronomical events," said Dr. Mac Low, a curator in the Museum's Department of Astrophysics. "We predicted that measurable changes could occur over times as short as a few decades."

The new study tested this theory with a 23-year-long experiment. The researchers used VLA observations of the Sagittarius B2 region made in 1989 and again in 2012. This massive star-forming region located near the Galactic center contains many small regions of ionized gas around high-mass stars, providing a large number of candidates for flickering. During this time, four of the HII regions indeed significantly changed in brightness.

"The long term trend is still the same, that HII regions expand with time," De Pree said. "But in detail, they get brighter or get fainter and then recover. Careful measurements over time can observe this more detailed process."

The publication can be viewed at: http://arxiv.org/abs/1312.7768

Kendra Snyder | EurekAlert!
Further information:
http://www.amnh.org

More articles from Physics and Astronomy:

nachricht Hubble observes one-of-a-kind star nicknamed 'Nasty'
22.05.2015 | NASA/Goddard Space Flight Center

nachricht Basel Physicists Develop Efficient Method of Signal Transmission from Nanocomponents
22.05.2015 | Universität Basel

All articles from Physics and Astronomy >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: Basel Physicists Develop Efficient Method of Signal Transmission from Nanocomponents

Physicists have developed an innovative method that could enable the efficient use of nanocomponents in electronic circuits. To achieve this, they have developed a layout in which a nanocomponent is connected to two electrical conductors, which uncouple the electrical signal in a highly efficient manner. The scientists at the Department of Physics and the Swiss Nanoscience Institute at the University of Basel have published their results in the scientific journal “Nature Communications” together with their colleagues from ETH Zurich.

Electronic components are becoming smaller and smaller. Components measuring just a few nanometers – the size of around ten atoms – are already being produced...

Im Focus: IoT-based Advanced Automobile Parking Navigation System

Development and implementation of an advanced automobile parking navigation platform for parking services

To fulfill the requirements of the industry, PolyU researchers developed the Advanced Automobile Parking Navigation Platform, which includes smart devices,...

Im Focus: First electrical car ferry in the world in operation in Norway now

  • Siemens delivers electric propulsion system and charging stations with lithium-ion batteries charged from hydro power
  • Ferry only uses 150 kilowatt hours (kWh) per route and reduces cost of fuel by 60 percent
  • Milestone on the road to operating emission-free ferries

The world's first electrical car and passenger ferry powered by batteries has entered service in Norway. The ferry only uses 150 kWh per route, which...

Im Focus: Into the ice – RV Polarstern opens the arctic season by setting course for Spitsbergen

On Tuesday, 19 May 2015 the research icebreaker Polarstern will leave its home port in Bremerhaven, setting a course for the Arctic. Led by Dr Ilka Peeken from the Alfred Wegener Institute, Helmholtz Centre for Polar and Marine Research (AWI) a team of 53 researchers from 11 countries will investigate the effects of climate change in the Arctic, from the surface ice floes down to the seafloor.

RV Polarstern will enter the sea-ice zone north of Spitsbergen. Covering two shallow regions on their way to deeper waters, the scientists on board will focus...

Im Focus: Gel filled with nanosponges cleans up MRSA infections

Nanoengineers at the University of California, San Diego developed a gel filled with toxin-absorbing nanosponges that could lead to an effective treatment for skin and wound infections caused by MRSA (methicillin-resistant Staphylococcus aureus), an antibiotic-resistant bacteria. This "nanosponge-hydrogel" minimized the growth of skin lesions on mice infected with MRSA - without the use of antibiotics. The researchers recently published their findings online in Advanced Materials.

To make the nanosponge-hydrogel, the team mixed nanosponges, which are nanoparticles that absorb dangerous toxins produced by MRSA, E. coli and other...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

International symposium: trends in spatial analysis and modelling for a more sustainable land use

20.05.2015 | Event News

15th conference of the International Association of Colloid and Interface Scientists

18.05.2015 | Event News

EHFG 2015: Securing health in Europe. Balancing priorities, sharing responsibilities

12.05.2015 | Event News

 
Latest News

Mesoporous Particles for the Development of Drug Delivery System Safe to Human Bodies

22.05.2015 | Materials Sciences

Computing at the Speed of Light

22.05.2015 | Information Technology

Development of Gold Nanoparticles That Control Osteogenic Differentiation of Stem Cells

22.05.2015 | Materials Sciences

VideoLinks
B2B-VideoLinks
More VideoLinks >>>