Stellar Evolution Archives

November 20, 2024November 20, 2024 by Evan Gough

Main Sequence and White Dwarf Binaries are Hiding in Plain Sight

This ALMA image shows the binary HD101584. The pair of stars share a common envelope, and are surrounded by complex clouds of gas. Image Credit: By ALMA, CC BY 4.0, https://commons.wikimedia.org/w/index.php?curid=86644758

Some binary stars are unusual. They contain a main sequence star like our Sun, while the other is a “dead” white dwarf star that left fusion behind and emanates only residual heat. When the main sequence star ages into a red giant, the two stars share a common envelope.

This common envelope phase is a big mystery in astrophysics, and to understand what’s happening, astronomers are building a catalogue of main sequence-white dwarf binaries.

October 16, 2024October 16, 2024 by Mark Thompson

Giant Cluster is Spitting Out Massive Stars

Artistic impression of star cluster R136 with runaway stars. Credit: Danielle Futselaar, James Webb Space Telescope/NIRCam - NASA, ESA, CSA and STScI

We live inside the Milky Way galaxy which is joined as it drifts through space by two satellite galaxies, the Magellanic Clouds. A star cluster in the Large Magellanic Cloud known as R136 has been the subject of a fascinating discovery. A team of astronomers have discovered 55 high-speed stars that have been ejected from the cluster. The discovery was made using the Gaia satellite and it seems up to a third of stars from the cluster have been ejected in the last century.

October 8, 2024October 8, 2024 by Carolyn Collins Petersen

The Open Star Cluster Westerlund 1, Seen by Webb

Here's Westerlund 1 in all its glory. This dense cluster of bright stars (with diffraction spikes from JWST's optics). They have a variety of sizes depending on their brightness and distance from us in the cluster, and different colors reflecting different types of star. Patches of billowing red gas can be seen in and around the cluster, lit up by the stars. Small stars in the cluster blend into a background of distant stars and galaxies on black. Courtesy ESA/Webb NASA & CSA, M. Zamani (ESA/Webb), M. G. Guarcello (INAF-OAPA) and the EWOCS team.

A long time ago, the Milky Way Galaxy was busy being a prodigious star-formation engine. In those times, it turned out dozens or hundreds of stars per year. These days, it’s rather more quiescent, cranking out only a few per year. Astronomers want to understand the Milky Way’s star-birth history, so they focus on some of the more recent star litters to study. One of them is Westerlund 1, a young so-called “super star cluster” that looks compact and contains a diverse array of older stars. It was part of a burst of star creation around 4 to 5 million years ago.

August 28, 2024August 28, 2024 by Mark Thompson

Is Betelgeuse Actually a Binary Star?

This image, made with the Atacama Large Millimeter/submillimeter Array (ALMA), shows the red supergiant Betelgeuse — one of the largest stars known. In the millimeter continuum the star is around 1400 times larger than our Sun. The overlaid annotation shows how large the star is compared to the Solar System. Betelgeuse would engulf all four terrestrial planets — Mercury, Venus, Earth and Mars — and even the gas giant Jupiter. Only Saturn would be beyond its surface. Link Betelgeuse captured by ALMA Scientific paper

Betel-gurz or Beetle-juice has been a favourite among amateur astronomers for many years. However you pronounce it, its unexpected dimming draw even more attention to this red supergiant variable star in Orion. It has a few cycles of variability, one of them occurs over a 2,170 day period, 5 times longer than its normal pulsation period. A paper has just been published that suggests a companion star of 1.17 solar masses could be the cause. It would need an orbit about 2.43 times the radius of Betelgeuse and it might just lead to the modulation of dust in the region that causes the variations we see.

July 18, 2024July 18, 2024 by Carolyn Collins Petersen

Stars Can Survive Their Partner Detonating as a Supernova

A binary star system consisting of two stars: a dense neutron star (lower right) and a normal Sun-like star (upper left). The neutron star formed in a supernova explosion and the Sun-like star survived it. Credit: Caltech/R. Hurt (IPAC)

When a massive star dies in a supernova explosion, it’s not great news for any planets or stars that happen to be nearby. Generally, the catastrophic event crisps nearby worlds and sends companion stars careening through space. So, astronomers were pretty surprised to find 21 neutron stars—the crushed stellar cores left over after supernova explosions—orbiting in binary systems with Sun-like stars.

May 17, 2024May 17, 2024 by Mark Thompson

Hubble Sees a Brand New Triple Star System

This NASA Hubble Space Telescope image captures a triple-star star system. NASA, ESA, G. Duchene (Universite de Grenoble I); Image Processing: Gladys Kober (NASA/Catholic University of America)

In a world that seems to be switching focus from the Hubble Space Telescope to the James Webb Space Telescope, Hubble still reminds us it’s there. Another amazing image has been released that shows the triple star system HP Tau, HP Tau G2, and HP Tau G3. The stars in this wonderful system are young, HP Tau for example is so young that it hasn’t started to fuse hydrogen yet and is only 10 million years old!

May 2, 2024May 2, 2024 by Allen Versfeld

Two Stars in a Binary System are Very Different. It's Because There Used to be Three

This image, taken with the VLT Survey Telescope hosted at ESO’s Paranal Observatory, shows the beautiful nebula NGC 6164/6165, also known as the Dragon’s Egg. The nebula is a cloud of gas and dust surrounding a pair of stars called HD 148937. Credit: ESO/VPHAS+ team. Acknowledgement: CASU

A beautiful nebula in the southern hemisphere with a binary star at it’s center seems to break our standard models of stellar evolution. But new data from the European Southern Observatory (ESO) suggests that there may once have been three stars, and that one was destroyed in a catastrophic collision.

April 15, 2024April 15, 2024 by Mark Thompson

Baby Stars Discharge “Sneezes” of Gas and Dust

The baby star at the center surrounded by a bright disk called a protostellar disk. Spikes of magnetic flux, gas, and dust in blue. Researchers found that the protostellar disk will expel magnetic flux, gas, and dust—much like a sneeze—during a star's formation.

I’m really not sure what to call it but a ‘dusty sneeze’ is probably as good as anything. We have known for some years that stars surround themselves with a disk of gas and dust known as the protostellar disk. The star interacts with it, occasionally discharging gas and dust regularly. Studying the magnetic fields revealed that they are weaker than expected. A new proposal suggests that the discharge mechanism ‘sneezes’ some of the magnetic flux out into space. Using ALMA, the team are hoping to understand the discharges and how they influence stellar formation.

February 6, 2024February 6, 2024 by Mark Thompson

Astronomers See 18 Examples of Stars Getting Torn Apart by Black Holes

MIT scientists have identified 18 new tidal disruption events (TDEs) — extreme instances when a nearby star is tidally drawn into a black hole and ripped to shreds. The detections more than double the number of known TDEs in the nearby universe. Credits:Credit: Courtesy of the researchers, edited by MIT News

Black holes have always held a special fascination for me ever since I was a geeky kid looking up at the stars. Their intense forces are the stuff of science fiction and can tear a star to pieces. This process is violent and can send bursts of electromagnetic radiation across the Cosmos. A paper recently published announces the discovery of 18 new tidal events just like this, doubling the number of identified shredded stars.

January 19, 2024January 19, 2024 by Evan Gough

Is this the Lightest Black Hole or Heaviest Neutron Star?

An international team of astronomers have found a new and unknown object in the Milky Way that is heavier than the heaviest neutron stars known and yet simultaneously lighter than the lightest black holes known. Image Credit: University of Manchester/Max Planck Institutue for Radio Astronomy

About 40,000 light-years away, a rapidly spinning object has a companion that’s confounding astronomers. It’s heavier than the heaviest neutron stars, yet at the same time, it’s lighter than the lightest black holes. Measurements place it in the so-called black hole mass gap, an observed gap in the stellar population between two to five solar masses. There appear to be no neutron stars larger than two solar masses and no black holes smaller than five solar masses.