NASA Finds Young Stars Dim in X-rays Surprisingly Quickly

Scientists have discovered that our Sun’s young stellar cousins ​​are calming down and decreasing their X-ray output more quickly than previously thought, according to a new study using NASA’s Chandra X-ray Observatory. A paper describing the results published Monday in The Astrophysical Journal.

Unlike the new movie “Project Hail Mary,” this calming of young stars is a benefit to the prospects for life on the planets orbiting these stars — not a threat.

Astronomers have used Chandra and other telescopes to monitor how powerful radiation from young stars – often in the form of dangerous X-rays – can hit the planets around them. They didn’t know how long this high-energy barrage would last, however.

This latest study focused on eight star clusters between 45 and 750 million years old. The researchers found that the Sun-like stars in these clusters released only about a quarter to a third of the X-rays they expected.

“While science fiction – like the Hail Mary Project microbes – imagines extraterrestrial life that dampens stellar production by consuming its energy, our real-world observations reveal a natural ‘quieting’ of young Sun-like stars in X-rays,” said Konstantin Getman, the lead author of the new study from Penn State University. “This is not because an external force is consuming their light, but because their internal generation of magnetic fields becomes less efficient.”

In fact, this relief could be a boon for the formation of life on planets around stars that are younger versions of our own Sun. (Our Sun is about 4.6 billion years old, much older than its stellar cousins ​​studied in this study.) Indeed, large amounts of X-rays can erode a planet’s atmosphere and prevent the formation of molecules necessary for organic life as we know it. On average, stars three million years old and with a mass equal to that of the Sun produce about a thousand times more X-rays than the current Sun. Meanwhile, solar-mass stars 100 million years old are about 40 times brighter in X-rays than today’s Sun.

“It’s possible that we owe our existence to the fact that our Sun is doing the same thing, several billion years ago, that we see these young stars doing now,” said co-author Vladimir Airapetian of NASA’s Goddard Space Flight Center in Greenbelt, Maryland. “This dimming of the real world echoes the dramatic stellar shift of fiction, but it may be even more fascinating because it sheds light on the real history of our own Sun.”

The researchers found that stars with roughly the same mass as the Sun quieted down relatively quickly – after a few hundred million years – while those with lower mass maintained their high levels of X-ray emission for longer. Combined with a decrease in X-ray energy and the disappearance of energetic particles, Sun-sized stars are apparently better suited than previously thought to host planets with robust atmospheres and possibly thriving life.

The research team also used data from the ESA (European Space Agency) Gaia satellite and x-ray data from the ROSAT mission (ROentgen SATellite). This data allowed them to identify the member stars of the clusters (and not the foreground or background stars). To measure the stars’ X-ray output, they made new Chandra observations of five clusters between 45 million and 100 million years old, in addition to using Chandra and ROSAT data from the archives to study three older clusters between 220 and 750 million years old.

Astronomers had not yet been able to study the X-ray production of stars in this age range. Most astronomers have relied on sparse data and a derived relationship that predicts the X-ray emission young stars should produce based on their age and rotation speed. Older, slower-rotating stars are generally fainter in X-rays, but the team found that X-ray output declines about 15 times faster than the derived relationship predicts during this specific phase of adolescence.

“We can only see our Sun at this precise moment in time, so to truly understand its past we need to look to other stars with roughly the same mass,” said co-author Eric Feigelson, also of Penn State University. “By studying X-rays from stars hundreds of millions of years old, we have filled an important gap in our understanding of their evolution.”

While they are still studying the cause of this slower-than-expected activity, scientists believe the process that generates the magnetic fields in these stars may become less efficient. This would lead to stars becoming quieter in X-rays more quickly, as they age. Researchers will continue to examine this and other potential causes of the rapid disappearance of young Sun-like stars.

NASA’s Marshall Space Flight Center in Huntsville, Alabama, manages the Chandra program. The Smithsonian Astrophysical Observatory’s Chandra X-ray Center controls science operations from Cambridge, Massachusetts, and flight operations from Burlington, Massachusetts.

Learn more about NASA’s Chandra X-ray Observatory

Learn more about the Chandra X-ray Observatory and its mission here:

https://science.nasa.gov/chandra

https://chandra.si.edu

Megan Watzke
Chandra X-ray Center
Cambridge, Mass.
617-496-7998
mwatzke@cfa.harvard.edu

Joel Wallace
Marshall Space Flight Center, Huntsville, Alabama
256-544-0034
joel.w.wallace@nasa.gov