SpaceWatch: spiral arms and space junk

Mars is space flavour of the month, with three spacecraft on their way and suggestions of a possible icy past, but there is other news of note. Here are some projects that took our fancy.

A stirred-up planet factory

Astrophysicists say planet-forming environments can be more complex and chaotic than previously thought if a new image of the star RU Lup, taken by the Atacama Large Millimeter / Submillimeter Array (ALMA) in Chile, is any guide.

All planets are born in discs of gas and dust around stars, so-called protoplanetary discs, and previous images have shown neatly arranged dusty discs with multiple rings and gaps that hint at the presence of emerging planets. Perhaps the most famous are of HL Tauri.

However, the new image of RU Lup, a young variable star in the Lupus constellation, reveals a giant set of spiral arms made of gas, extending far beyond its more well-known dust disk.

The structure, resembling a mini-galaxy, extends to nearly 1000 astronomical units (au) from the star, much farther away than the compact dust disc that extends to about 60 au.

“The fact that we observed this spiral structure in the gas after a longer observation suggests that we have likely not seen the full diversity and complexity of planet-forming environments,” says Jane Huang from the Centre for Astrophysics, Harvard & Smithsonian, lead author on a paper in The Astrophysical Journal.

“We may have missed much of the gas structures in other discs.”

Huang and her team suggest possible scenarios to explain the spiral arms: the disc might be collapsing under its own gravity; RU Lup might be interacting with another star; or the disc might be interacting with its environment, accreting interstellar material along the spiral arms.

However, “[n]one of these scenarios completely explain what we have observed,” says co-author Sean Andrews.

A rare, tiny galaxy rather low on oxygen

Astronomers using the Subaru Telescope, the WM Keck Observatory and a new method of machine learning have discovered a nearby galaxy they say breaks the record for having the lowest level of oxygen ever seen.

They measured the oxygen abundance of HSC J1631+4426 as only 1.6% that of the Sun, suggesting it only recently started making stars, which is rare. Most galaxies in the modern Universe are already mature.

The galaxy is just 430 million light-years away in the constellation Hercules, and it’s tiny, according to Masami Ouchi from the National Astronomical Observatory of Japan, co-author of a paper in The Astrophysical Journal.

“What’s surprising is the stellar mass of the HSC J1631+4426 galaxy is very small, 0.8 million solar masses, which is only about 1/100,000 of our Milky Way, and comparable to the mass of a star cluster in our galaxy.”

The Subaru made the discovery possible, but also a little tricky, because it detected 40 million objects.

To comb through the vast amount of data and zero in on galaxies that are just beginning to form stars, the researchers taught a computer to repeatedly learn the galaxy colours expected from theoretical models and select only those galaxies in the early stage of formation.

“Low-mass, young, metal-poor galaxies found near us are important because they resemble primordial galaxies, making HSC J1631+4426 one of the best local labs for studying in detail what the first galaxies were like in the early Universe, shortly after the Big Bang,” says John O’Meara, chief scientist at Keck Observatory.

Space junk spotting opens up

We may soon be able to chase space junk pretty well 24/7. European researchers led by the Austrian Space Research Institute have increased the value and potential of what’s known as space debris laser ranging by greatly expanding its working hours.

The technique measures the distance to stray objects in space, but is currently only possible for a few hours around twilight, when the observation station on Earth is in darkness but the debris is still illuminated by the Sun.

However, Michael Steindorfer and colleagues say they have combined a telescope, detector and filter to increase the contrast of objects with respect to the daylight sky, and also developed real-time target detection software that calculates the target-prediction offset, which is then used to correct inaccurate predictions.

Writing in the journal Nature Communications, they suggest that observation times at the space laser ranging station in Graz could now increase from 6 to 22 hours a day, depending on the season, allowing for more precise orbital predictions and thus greater safety for satellite and space station operations in Earth’s orbit.