The youngest neutron star detected so far turned 37 years old last week. To celebrate, James Webb Space Telescope has finally found the most direct evidence of it, hiding among the remains of the supernova cloud it was born in.
Usually when we’re talking about the age of astronomical objects, it’s in the millions or billions of years – so finding something that’s younger than Lady Gaga feels weird. Even weirder is being able to trace its birth to a specific date – February 23, 1987, meaning it just clocked over to its 37th birthday last Friday.
The reason we can so confidently pinpoint the date is because its birth was the result of an event that only happens once every few centuries: a supernova that’s close enough to be observed from Earth with the naked eye. SN 1987A lit up the night sky for a few months in early 1987, and was quickly traced to the Large Magellanic Cloud, a dwarf galaxy orbiting the Milky Way, about 168,000 light-years away. There, a blue supergiant star appeared to have collapsed and exploded, which should have left either a black hole or a neutron star.
Astronomers have been searching for signs of the object ever since, with surprisingly little success. In 2019 a team from Cardiff University found that a particular patch of dust in the cloud was shining a bit brighter in certain wavelengths of light than the rest. Others have also found similar indirect evidence, but a new study has now found the most direct evidence to date that a baby neutron star lives there.
The key to the discovery, as with so many recently, is the James Webb Space Telescope. Astronomers used its infrared instruments to analyze the spectrum of the gas and dust in the SN 1987A cloud, which revealed the presence of argon that had been ionized five times over – essentially, that means the atoms have been stripped of five of their 18 electrons. This process would require very energetic photons, which should be a smoking gun for a neutron star.
“To create these ions that we observed in the ejecta, it was clear that there had to be a source of high-energy radiation in the center of the SN 1987A remnant,” said Claes Fransson, lead author of the study. “In the paper we discuss different possibilities, finding that only a few scenarios are likely, and all of these involve a newly born neutron star.”
So happy 37th birthday, probable-neutron-star-of-SN-1987A! While a human of that age would probably be preparing for a midlife crisis, it’s barely the first breath for a neutron star that could shine for billions of years yet.
To save our comments section from the wrath of "well actuallys," let's just acknowledge those caveats about the claim. First, yes, we understand that technically speaking this neutron star is 168,037 years old, given the distance. But as soon as you start adjusting for time like that, things start to get messy. It's common usage, and far neater, to describe things based on our perspective here on Earth, given it's the only one we've got. Don't take it out on us if the Glorxians living in the LMC have known about it for 168 millennia.
Second, new neutron stars are being born all over the universe constantly, so technically the record for youngest neutron star would have been shattered seconds after SN 1987A. But we're talking about the youngest directly detected by us humans, which allows us to study the very early days of their life cycle.
The research was published in the journal Science.
