A new understanding of young stars can help us hunt for life in space

The Sun is a middle-aged star. It’s already affirmed its identity, cares less about the opinions of others, and is a lot less energetic.

During its younger years, the Sun would eject flares of hot plasma into outer space, generating energetic outbursts that would often reach its orbiting planets.

In order to get a view of what the Sun may have acted like millions of years ago, a team of scientists observed thousands of young stars. They found that young stars can have a positive and negative effect on the habitability of their orbiting planets, which may help scientists in their hunt for exoplanets that accompany distant stars.

Their findings are detailed in a study that was accepted for publication in The Astrophysical Journal.

“They were just, wow, they were humongous and very frequent — it's unbelievable.”

WHAT’S NEW — Using NASA's Chandra X-ray Observatory, the team of scientists conducted the largest survey of star-forming regions.

They covered some 24,000 individual stars in 40 different regions, all of which were under the cosmic age of 5 million years. In comparison, the Sun is around 4.5 billion years old.

The scientists observed the flareups of the young stars. Flares are when stars eject boiling hot plasma and high-intensity eruptions from their surface that result in stellar outbursts.

The survey found that the young stars’ flares are at least 100,000 times more energetic than the Sun’s most energetic outbursts. The study compared the flare-ups to the Carrington Event in 1859, a geomagnetic storm that occurred after a coronal mass ejection hit Earth’s magnetosphere, causing a blackout in many parts of the world and wreaking havoc on the telegraph system.

The young stars’ super-flares were at least one hundred thousand times more energetic than the Carrington Event and their mega-flares were up to 10 million times more energetic. Super-flares occurred once every week on average for each star, and about two mega flares occurred every year, according to the study.

Konstantin Getman, a research professor at Pennsylvania State University and lead author of the new study, looks back at what a young Sun may have looked like 5 million years ago.

“God, those flares!” Getman tells Inverse. “They were just, wow, they were humongous and very frequent — it's unbelievable.”

These flare-ups were observed all over the star-forming regions and throughout the different evolutionary stages of the stars. This means the flares occurred while the star was surrounded by clouds of leftover material shortly after its formation, when proto-planets began to coalesce, and even after the planets have formed.

WHY IT MATTERS — The study suggests that the Sun may have affected the young Earth billions of years ago, possibly in relation to our planet’s habitability.

Through their observations, the researchers found that the young stars had both a positive and a negative effect on their orbiting planets.

• On the positive note, these stellar flares drive gas away from disks of material that surround the stars and form pebbles and other small rocky material from which planets form.
• On the other hand, these outbursts of high-energy radiation can also eat away at planets’ atmospheres, resulting in the destruction of the planet in about 5 million years.

“We're learning that the environment was very harsh during the first 5 million years,” Getman says.

What’s next — When the Sun was a young star, it would not have fueled our existence on Earth.

As we look for habitability, and possible life forms on other planets, scientists tend to stay away from young, active stars for that reason. As the study shows, it would not be possible to sustain life on a planet orbiting a newly formed star. Researchers will dig into the implications as the quest for life beyond Earth widens.

“I didn't live on such a young planet, but if I did, it's pretty much probably impossible to exist within such volatile environments,” Getman says. “We would not survive.”

Abstract: Solar-type stars exhibit their highest levels of magnetic activity during their early convective pre-main sequence (PMS) phase of evolution. The most powerful PMS flares, super-flares and mega-flares, have peak X-ray luminosities of log(LX)=30.5−34.0~erg~s−1 and total energies log(EX)=34−38~erg. Among >24,000 X-ray selected young (t<5~Myr) members of 40 nearby star-forming regions from our earlier Chandra MYStIX and SFiNCs surveys, we identify and analyze a well-defined sample of 1,086 X-ray super-flares and mega-flares, the largest sample ever studied. Most are considerably more powerful than optical/X-ray super-flares detected on main sequence stars. This study presents energy estimates of these X-ray flares and the properties of their host stars. These events are produced by young stars of all masses over evolutionary stages ranging from protostars to diskless stars, with the occurrence rate positively correlated with stellar mass. Flare properties are indistinguishable for disk-bearing and diskless stars indicating star-disk magnetic fields are not involved. A slope α≃2 in the flare energy distributions dN/dEX∝E−αX is consistent with those of optical/X-ray flaring from older stars and the Sun. Mega-flares (log(EX)>36.2~erg) from solar-mass stars have occurrence rate of 1.7+1.0−0.6 flares/star/year and contribute at least 10−20\% to the total PMS X-ray energetics. These explosive events may have important astrophysical effects on protoplanetary disk photoevaporation, ionization of disk gas, production of spallogenic radionuclides in disk solids, and hydrodynamic escape of young planetary atmospheres. Our following paper details plasma and magnetic loop modeling of the >50 brightest X-ray mega-flares.