Skip to main content

You Don't Want to Be Within 160 Light-Years of a Supernova

Supernovae are incredibly common in the universe. Based on observations of isotopes such as aluminum-26, we know that a supernova occurs on average about every fifty years in the Milky Way alone. A supernova can outshine a galaxy, so you wouldn’t want your habitable planet to be a few light years away when it goes off. Fortunately, most supernovae have occurred very far away from Earth, so we haven’t had to concern ourselves with wearing sunscreen at night. But it does raise an interesting question. When it comes to supernovae, how close is too close? As a recent study shows, the answer depends on the type of supernova.

There is geological evidence that supernovae have occurred quite close to Earth in the past. The isotope iron-60 has a half-life of just 2.6 million years, and it has been found in ocean floor sediment laid down about 2 million years ago. It has also been found in Antarctic ice cores and lunar regolith, suggesting a supernova event around that time. Samples of Earth’s crust point to evidence of another supernova event around 8 million years ago. Both of these would likely have occurred within a few hundred light years of Earth, perhaps as close as 65 light years. Neither of these supernovae seems to have triggered a planet-wide mass extinction, so you might think any supernova more distant than 100 light years is harmless.

The habitable zone for the Milky Way galaxy. Credit: NASA/JPL-Caltech/R. Hurt (SSC/Caltech)

This new study suggests otherwise. Earlier studies focused on two dangerous periods of a supernova: the overall brightness of the initial explosion reaching a planet at the speed of light, and the stream of energized particles that can strike the planet hundreds or thousands of years later. Both of these tend to have weak effects over hundreds of light years. A nearby supernova might outshine the Moon for a time, which would affect the nocturnal patterns of some creatures, but it wouldn’t trigger mass extinctions. Likewise, our atmosphere is a good barrier to cosmic rays, thus a burst of them for a time is relatively harmless. But this study looked specifically at X-ray light emitted by some supernova, and this is where things can get worse.

X-rays are particularly good at disrupting things like ozone. A strong beam of X-rays from a supernova could strip the ozone layer from a planet like Earth, leaving it open to ultraviolet radiation from its Sun. The ultraviolet light could trigger the creation of a smog layer of nitrogen dioxide, which would lead to acid rain and a wide-scale de-greening of the planet.

The habitable zone for the Milky Way galaxy depends on several factors. Credit: Lineweaver, et al

So the lethal distance of a supernova depends not only on its proximity to a habitable planet but also on the level of X-rays it generates. The team looked at the X-ray spectra of nearly three dozen supernovae over the last 45 years and calculated the lethal distance for each of them. The most harmless was the popular 1987a supernova, which was safe within a light-year or so. The most potentially deadly was a supernova named 2006jd, which could kill a habitable planet from up to 160 light years away.

To be clear, there is no nearby star that poses a potential threat to Earth, not even Betelgeuse. But this study helps us better define where habitable planets might survive in our galaxy. Just as a habitable planet can’t be too close to its star, a planetary system can’t be too close to areas where supernovae are most common, such as the center of our galaxy.

Reference: Brunton, Ian R., et al. “X-Ray-luminous Supernovae: Threats to Terrestrial Biospheres.” The Astrophysical Journal 947.2 (2023): 42.

Reference: Lineweaver, Charles H., Yeshe Fenner, and Brad K. Gibson. “The galactic habitable zone and the age distribution of complex life in the Milky Way.” Science 303.5654 (2004): 59-62.

The post You Don't Want to Be Within 160 Light-Years of a Supernova appeared first on Universe Today.



from Universe Today https://ift.tt/TgxWJHj
via IFTTT

Comments

Popular posts from this blog

Researchers Match Up 12 Meteorites with the Near-Earth Asteroids They Came From

Every day meteoroids blast through our planet’s atmosphere to hit the ground as meteorites. A team of researchers in Italy traced twelve of them to progenitor asteroids that orbit in near-Earth space. Scientists treasure meteorites because they reveal information about their parent bodies. In an arXiv paper, two Italian researchers—Albino Carbognani and Marco Fenucci—analyze the characteristics of the parent bodies of 20 selected meteorites. They were able to track all but eight back to their parent asteroids. Based on their work, the pair says at least a quarter of meteorites come from collisions that happened in near-Earth space and not in the Main Belt. Meteorites from Near-Earth Asteroids: How They Got Here Many meteorites are chondritic, similar to asteroids in the Main Belt (or came from it). In their paper, the authors point out that progenitor meteoroids (including many that fall to Earth and become meteorites) formed millions of years ago following collisions between main-...

JWST Takes a Detailed Look at Jupiter’s Moon Ganymede

Nature doesn’t conform to our ideas of neatly-contained categories. Many things in nature blur the lines we try to draw around them. That’s true of Jupiter’s moon Ganymede, the largest moon in the Solar System. The JWST took a closer look at Ganymede, the moon that’s kind of like a planet, to understand its surface better. Ganymede is basically a planet, except it doesn’t orbit the Sun. If it did orbit the Sun instead of Jupiter, it would be indistinguishable from a planet. It has a differentiated internal structure with a molten core that produces a magnetic field. It has a silicon mantle much like Earth’s, and has a complex icy crust with a deep ocean submerged beneath it. It has an atmosphere, though it’s thin. It’s also larger than Mercury, and almost as large as Mars. According to the authors of a new study, it’s an archetype of a water world. But even with all this knowledge of the huge moon, there are details yet to be revealed. This is especially true of its complex surface...

What Blew Up the Local Bubble?

In our neighborhood of the Milky Way, we see a region surrounding the solar system that is far less dense than average. But that space, that cavity, is a very irregular, elongated shape. What little material is left inside of this cavity is insanely hot, as it has a temperature of around a million Kelvin. from Universe Today https://ift.tt/KvVDeiC via IFTTT