SpaceWatch: News of gas and asteroids

Magnetised “rivers” feed star birth

Stars form when clouds of gas and dust collapse under gravity, but how does the material get to the clouds from interstellar space, and what controls their collapse?

This image from the Stratospheric Observatory for Infrared Astronomy (SOFIA) in the US throws some light onto the subject. It shows narrow, spindle-like structures called filaments, that act like rivers channelling material into the Serpens South cluster, a group of more than 60 young stars forming in a dense cloud of gas and dust nearly 1400 light-years away.

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Composite image of the Serpens South Cluster. Credit: NASA/SOFIA/T Pillai; NASA/JPL-Caltech/L Allen

The fields, shown as streamlines over an image from NASA’s retired Spitzer Space Telescope, have been dragged by gravity to align with the narrow, dark filament on the lower left – helping material flow down it. In the upper parts of the image, the magnetic fields are perpendicular to the filaments as they oppose gravity.

Scientists are studying the dense cloud to learn how magnetic fields, gravity and turbulent gas motions contribute to the creation of stars. It was once thought magnetic fields slow star birth by counteracting gravity, but the new data suggest they may actually be working together with gravity as it pulls the fields into alignment with the filaments, nourishing the birth of stars.

The research was led by Thushara Pillai, from Boston University, US, and is published in the journal Nature Astronomy.

Debris moving fast after 400 years

A sequence of images taken over nearly a decade and a half by NASA’s Chandra X-ray Observatory has captured pieces of debris from the Kepler supernova remnant still moving at up to 36 million kilometres per hour (kph) more than 400 years after the explosion was spotted by early astronomers.

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Credit: NASA/CXC/Univ of Texas at Arlington/M. Millard et al

The Kepler remnant is the aftermath of a Type Ia supernova, where a white dwarf – a small dense star – exceeds a critical mass limit after interacting with a companion star and undergoes a thermonuclear explosion that shatters it and launches its remains outward.

The latest study tracked the speed of 15 small “knots” of glowing debris. The top speed was the fastest for supernova remnant debris ever recorded in X-rays. The average was an impressive 16 million kph, and the blast wave is expanding at about 24 million kph.

These results independently confirm the 2017 discovery of knots travelling at speeds more than 32 million kph in the Kepler supernova remnant, the researchers write in a paper the Astrophysical Journal.

Scientists are still trying to determine whether an extremely powerful explosion or an unusual environment around it is responsible for these high speeds so long after the explosion.

A Near Earth Asteroid that really was

NASA announced this week that an SUV-size space rock it detected over the weekend came closer to Earth than any previous known Near Earth Asteroid (NEA), passing just 2950 kilometres above the southern Indian Ocean.

2020 QG is very small by asteroid standards, at roughly three metres by six, and if it had actually been on an impact trajectory, it would likely have become a fireball as it broke up in Earth’s atmosphere – which happens several times a year.

By some estimates, there are hundreds of millions of asteroid of a similar size, but they are extremely hard to discover until they get very close to Earth. The vast majority of NEAs pass by safely at much greater distances – usually much farther away than the Moon.

“It’s really cool to see a small asteroid come by this close, because we can see the Earth’s gravity dramatically bend its trajectory,” says Paul Chodas, director of NASA’s Centre for Near-Earth Object Studies (CNEOS). “Our calculations show that this asteroid got turned by 45 degrees or so as it swung by our planet.”

It was moving at more than 12 kilometres a second – a little slower that average.

Asteroid 2020 QG’s trajectory bending during its close approach to Earth. Credit: NASA/JPL-Caltech

Milky Way expelling gas – rapidly

Astronomers say they have discovered a dense, cold gas that’s been shot out from the centre of the Milky Way “like bullets”.

Exactly how remains a mystery, but the international team says its findings, published in the journal Nature, could have important implications for the future of our galaxy.

“Galaxies can be really good at shooting themselves in the foot,” says co-author Naomi McClure-Griffiths from the Australian National University.

“When you drive out a lot of mass, you’re losing some of the material that could be used to form stars, and if you lose enough of it, the galaxy can’t form stars at all anymore.

“So, to be able to see hints of the Milky Way losing this star forming gas is kind of exciting – it makes you wonder what’s going to happen next!”

The centre of the Milky Way is home to a massive black hole, but it’s unclear whether this has expelled the gas, or whether it was blown by the thousands of massive stars at the centre of the galaxy.

“We don’t know how either the black hole or the star formation can produce this phenomenon,” says lead author Enrico Di Teodoro from Johns Hopkins University, US.

“We’re still looking for the smoking gun, but it gets more complicated the more we learn about it. 

“This is the first time something like this has been observed in our galaxy. We see these kind of processes happening in other galaxies. But, with external galaxies you get much more massive black holes, star formation activity is higher, it makes it easier for the galaxy to expel material.

The gas was observed using the Atacama Pathfinder EXperiment (APEX) operated by the European Southern Observatory in Chile.

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The Atacama Pathfinder Experiment. Credit: ESO/B Tafreshi/TWAN

Replicating high densities in white dwarfs

For the first time, scientists have found a way to describe conditions deep in the convection zone of “white dwarf” stars.

Working at the National Ignition Facility in the US, researchers from the US, Germany and Canada simulated the crushing pressure created as stars cease to produce their own fuel, leaving only an extremely dense core.

They fired nanometre laser light into a hohlraum (a tiny gold cylinder), bathing a one-millimetre sample of a carbon-based compound in radiation heated to nearly 3.5 million degrees, at pressures ranging from 100 to 450 million atmospheres.

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Credit: Mark Meamber/Lawrence Livermore National Laboratory

“This is the first time we have been able to lock down an equation of state, describing the behaviour of matter that is intrinsic to white dwarf stars, in particular the regime in a part of white dwarfs where oscillations occur that have been particularly difficult to model,” says Gilbert Collins from the University of Rochester, a co-author of a paper in Nature.

White dwarfs, which contain some of the densest collections of matter in the Universe, are what stars become after they have exhausted their nuclear fuel and expelled most their outer material. The process leaves behind a hot core that cools down over the next billion years or so.

A recent analysis has suggested that white dwarfs are an important source of carbon found in galaxies.

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