Categories: Space

Evidence Supports Solution to 30-Year-Old Puzzle of Massive Star Formation

Astronomers Solve 30 Year Puzzle of Massive Star Formation

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

Using the Jansky Very Large Array, astronomers have discovered evidence supporting a solution to a 30-year puzzle about the birth of massive stars.

An international group of astrophysicists including Museum Curator Mordecai-Mark Mac Low 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.

Now, observations made by a team of researchers using the Jansky Very Large Array (VLA), a radio astronomy observatory in New Mexico, have confirmed predictions 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.

“Massive stars dominate the lives of their host galaxies through their ionizing radiation and supernova explosions,” said Dr. Mac Low, a curator in the Department of Astrophysics. “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.”

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.

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. “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.”

Publication: C. G. De Pree, et al., “Flickering of 1.3 cm Sources in Sgr B2: Towards a Solution to the Ultracompact HII Region Lifetime Problem,” 2014, ApJ, 781, L36; doi:10.1088/2041-8205/781/2/L36

PDF Copy of Study: Flickering of 1.3 cm Sources in Sgr B2: Towards a Solution to the Ultracompact HII Region Lifetime Problem

Image: NRAO/Agnes Scott College

Share

Recent Posts

NASA Assesses Launch Pad for Damage After Launch of the World’s Most Powerful Rocket

Following the successful Artemis I liftoff of the world’s most powerful rocket from NASA’s Kennedy…

November 29, 2022

History-Making Event: Orion Goes the (Max) Distance – 268,563 Miles From Earth

NASA Artemis I — Flight Day 13: Orion Goes the (Max) Distance Just after 3…

November 29, 2022

Autism Breakthrough: New Treatment Significantly Improves Social Skills and Brain Function

The treatment caused neurological changes, including a decrease in inflammation and an increase in functionality,…

November 29, 2022

Seemingly Impossible: Nanostructure Compresses Light 10,000 Times Thinner Than a Human Hair

This major scientific advance has implications for many fields, including energy-efficient computers and quantum technology.…

November 29, 2022

“Profound Implications” – New Research Details the Microbial Origins of Type 1 Diabetes

A bacterial protein stimulates the reproduction of insulin-producing cells, pointing to a potential treatment. Nearly…

November 29, 2022

Scientists Develop an “Extended Landau Free Energy Model” for Advanced Materials Design

Explainable AI-Based Physical Theory for Advanced Materials Design Scientists develop an “extended Landau free energy…

November 29, 2022