When massive stars die, they don’t do it quietly.
Their deaths are spectacularly brilliant affairs that light up the cosmos, a supernova explosion that sends guts of stars into space in a cloud of splendor. Meanwhile, the star’s core that was may linger, collapsed into an ultra-dense neutron star or black hole.
If this explosion happens in a certain way, it can send the collapsed core through the Milky Way like a bat out of hell, at such insane speeds that they can eventually fly out of the galaxy altogether, when of a wild journey through intergalactic space. .
It’s one of those objects just measured using data from the Chandra X-ray Observatory: a type of pulsating neutron star known as a pulsar, tearing through its own innards at a speed approximately 612 kilometers per second (or 1.4 million miles per hour).
It is one of the fastest such objects ever detected. (The fastest known star in the Milky Way is not a supernova remnant that was hit by an explosion, but a star orbiting Sgr A*, the supermassive black hole at the center of the galaxy. fastest point in its orbit, it is moving at a wild 24,000 kilometers per second.)
“We saw the movement of the pulsar directly in the X-rays, which we could only do with Chandra’s very sharp vision,” said astrophysicist Xi Long of the Harvard & Smithsonian Center for Astrophysics (CfA).
“Because it’s so distant, we had to measure the equivalent of a quarter width at about 15 miles to see this movement.”
The detection was made by looking at a glowing supernova remnant about 20,000 light-years away, named G292.0+1.8. Previous observations had revealed a fast pulsar there. Long and his colleagues wanted to study the object to see if it could reveal the supernova’s history, tracing its motion toward the center of the object in reverse.
“We only have a handful of supernova explosions that also have a reliable historical record,” said CfA astrophysicist Daniel Patnaude, “so we wanted to check if G292.0+1.8 could be added to this band”.
They studied images taken of the supernova remnant in 2006 and 2016 and used Gaia’s data on its current location in the Milky Way, comparing differences in the pulsar’s position. These comparisons revealed something extremely interesting: the dead star appears to be moving 30% faster than previous estimates suggested.
This means that it took much less time to travel from the center of the supernova remnant, suggesting that the supernova itself took place much more recently. Previous estimates place the date of the supernova at around 3,000 years ago; the new estimates date back about 2,000 years.
The revised speed of the pulsar also allowed the team to carry out a detailed new investigation of how the dead star could have been ejected from the center of the supernova. They proposed two scenarios, both involving a similar mechanism.
In the first, neutrinos are ejected from the supernova explosion asymmetrically. In the other, debris from the explosion is ejected asymmetrically. However, since the neutrino energy is expected to be extremely large, the most likely explanation is asymmetric debris.
Basically, an unbalanced explosion can “throw” the collapsed core of a dead star into space at extremely high speeds; in this case, the star is currently moving at a speed greater than the Milky Way’s mid-disc escape velocity of 550 kilometers per second, although it will take some time to get there, and it could slow down with time.
In fact, its actual speed may even be over 612 kilometers per second, as it moves ever so slightly along our line of sight.
“This pulsar is about 200 million times more energetic than the motion of the Earth around the Sun,” said CfA astrophysicist Paul Plucinsky. “It seems to have received its powerful kick simply because the supernova explosion was asymmetrical.”
The team’s research, presented at the 240th meeting of the American Astronomical Society, has been accepted into The Astrophysical Journal and is available on arXiv.