A supernova – or exploding star – is one of our galaxy’s most cataclysmic events. It’s long been known that supernovae can obliterate super-close planets, if there are any. Now, scientists have released new findings showing that supernovae can be dangerous to habitable planets farther away, too. Chandra X-ray Observatory said this month (April 20, 2023) that the newly identified threat involves a phase of intense X-rays that can damage the atmospheres of planets up to 160 light-years away.

“Damage the atmospheres.” That means that, for any habitable or even inhabited planets, a nearby supernova could dramatically alter life’s prospects. Lucky for Earth that no potential supernova progenitors within 160 light-years.

On the other hand, Earth might have experienced this kind of X-ray exposure in the past.

The researchers who discovered this detail are with NASA’s Chandra X-ray Observatory and other X-ray telescopes. The Astrophysical Journal published the team’s peer-reviewed results on April 19, 2023.

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Supernova known dangers

Until now, astronomers knew about two particular kinds of danger from supernovae to planets orbiting nearby stars. The first is the intense radiation produced by a supernova blast. That radiation can last for days or months, after the initial explosion.

Energetic particles are the second danger. Since – unlike the radiation mentioned just above – the particles don’t travel at the speed of light, there’s a delay for planets receiving this. The energetic particles might hit a nearby planet hundreds or thousands of years after the supernova blast. The new research paper says:

The spectacular outbursts of energy associated with supernovae … have long motivated research into their potentially hazardous effects on Earth and analogous environments. Much of this research has focused primarily on the atmospheric damage associated with the prompt arrival of ionizing photons within days or months of the initial outburst, and the high-energy cosmic rays that arrive thousands of years after the explosion.

And, now, researchers point to a third danger: X-rays. They knew supernovae produce X-rays. But new evidence from the X-ray telescopes shows the X-rays can be larger and more lethal than once thought.

How does it happen? When the blast wave from a supernova hits a cloud of dense gas, it can produce a larger dose of X-rays. The effects of the X-rays can last for decades. This intense dose of X-rays can affect planets orbiting stars up to 160 light-years away.

Observations from multiple X-ray telescopes

The researchers made the discovery using NASA’s Chandra, Swift and NuSTAR space telescopes, as well as ESA’s (European Space Agency’s) XMM-Newton.

They observed 31 supernovae for the new study.

So the X-rays from supernovae could significantly damage a planet’s atmosphere up to a 160 light-year distance. And, the scientists said, the damage would be especially bad for habitable planets. If the damage to the planet’s atmosphere were extensive enough, it could cause an extinction event for any life already dwelling there. Lead author Ian Brunton of the University of Illinois at Urbana-Champaign commented:

If a torrent of X-rays sweeps over a nearby planet, the radiation would severely alter the planet’s atmospheric chemistry.

For an Earth-like planet, this process could wipe out a significant portion of ozone, which ultimately protects life from the dangerous ultraviolet radiation of its host star.

Is Earth in danger from supernovae?

Is Earth in danger? The researchers say no, because there are no stars near enough that would be expected to explode. Co-author Connor O’Mahoney, also from the University of Illinois, reassured people, saying:

The Earth is not in any danger from an event like this now, because there are no potential supernovae within the X-ray danger zone. However, it may be the case that such events played a role in Earth’s past.

The scientists pointed to supernovae occurring between 2 and 8 million years ago, between about 65 and 500 light-years of Earth. The stars exploded as supernova then would have been much closer to Earth similar stars are now.

That’s good news for us now. But it wasn’t good news for any living creatures on Earth, millions of years ago.

An earlier study, released in 2021, had suggested we’d need to be within 50 light-years of a supernova to feel its effects.

But, even before that, a study from 2016 had shown that supernovae less than 300 light-years away once showered Earth with radioactive debris. Scientists estimate the debris hit Earth between 3.2 and 1.7 million years ago.

Supernovae such as these could also shrink the Galactic Habitable Zone. Those are the regions, collectively, where planets would be safe enough for life to flourish.

As always more research needed

The new findings provide important data about supernovae and their effects on their surroundings. But more observations are needed, as co-author Brian Fields of the University of Illinois noted:

Further research on X-rays from supernovae is valuable not just for understanding the life cycle of stars, but also has implications for fields like astrobiology, paleontology and the earth and planetary sciences.

The paper further explained:

We urge follow-up X-ray observations of interacting SNe for months and years after the explosion to shed light on the physical nature and full-time evolution of the emission and to clarify the danger that these events pose for life in our galaxy and other star-forming regions.

Bottom line: Researchers using NASA’s Chandra X-ray Observatory and other telescopes say that supernovae are even more dangerous to habitable planets than first thought.

Source: X-Ray-luminous Supernovae: Threats to Terrestrial Biospheres

Via Chandra X-ray Observatory