Cambridge, Mass. – A young pulsar crosses the Milky Way at a speed of more than a million miles per hour. This stellar speedster, observed by NASA’s Chandra X-ray Observatory, is one of the fastest such objects ever seen. This result tells astronomers more about how some of the largest stars end their lives.
Pulsars are rapidly rotating neutron stars that form when certain massive stars run out of fuel, collapse, and explode. This pulsar passes through the remnants of the supernova explosion that created it, called G292.0+1.8, located about 20,000 light-years from Earth.
“We directly saw the movement of the pulsar in the X-rays, which we could only do with Chandra’s very sharp vision,” said Xi Long of the Center for Astrophysics | Harvard & Smithsonian (CfA), which conducted the study. “Because it’s so distant, we had to measure the equivalent of a quarter width at about 15 miles to see this movement.”
To make this discovery, the researchers compared Chandra images of G292.0+1.8 taken in 2006 and 2016. Based on the pulsar’s change in position over a 10-year period, they calculated that it is moving by at least 1.4 million miles per hour from the center of the lower left supernova remnant. This speed is about 30% higher than a previous estimate of the pulsar’s speed which was based on an indirect method, by measuring the distance between the pulsar and the center of the explosion.
The newly determined speed of the pulsar indicates that G292.0+1.8 and its pulsar could be much younger than astronomers previously thought. Xi and his team estimate that G292.0+1.8 would have exploded around 2,000 years ago as seen from Earth, rather than 3,000 years ago as previously calculated. Several civilizations around the world were recording supernova explosions at this time, opening up the possibility that G292.0+1.8 was directly observed.
“We only have a handful of supernova explosions that also have a reliable historical record linked to them,” said co-author Daniel Patnaude, also from CfA, “so we wanted to check if G292.0 +1.8 could be added to this group.”
However, G292.0+1.8 is below the horizon for most northern hemisphere civilizations that might have observed it, and there are no recorded examples of a supernova observed in the southern hemisphere in the direction of G292.0 + 1.8.
Along with finding out more about the age of G292.0+1.8, the research team also looked at how the supernova gave the pulsar its mighty kick. There are two main possibilities, both of which imply that matter is not ejected uniformly by the supernova in all directions. One possibility is that neutrinos produced in the explosion are ejected from the explosion asymmetrically, and the other is that debris from the explosion is ejected asymmetrically. If the material has a preferred direction, the pulsar will be thrown in the opposite direction due to the principle of physics called conservation of momentum.
The amount of neutrino asymmetry needed to explain the high speed of this latter result would be extreme, supporting the explanation that asymmetry in the debris from the explosion kicked the pulsar. This agrees with a previous observation that the pulsar is moving in the opposite direction to the mass of the x-ray emitting gas.
The energy transmitted to the pulsar by this explosion was gigantic. Although it is only about 10 miles in diameter, the mass of the pulsar is 500,000 times that of Earth and it is moving 20 times faster than the speed of Earth orbiting the Sun.
“This pulsar is about 200 million times more energetic than the motion of the Earth around the Sun,” said co-author Paul Plucinsky, also from CfA. “It seems to have received its powerful kick simply because the supernova explosion was asymmetrical.”
The actual speed in space is likely to be over 1.4 million miles per hour because the imaging technique only measures movement from side to side, rather than along our line of motion. aimed at the pulsar. An independent Chandra study of G292.0+1.8 by Tea Temim of Princeton University suggests that the speed along the line of sight is about 800,000 miles per hour, giving a total speed of 1. 6 million miles per hour. A paper describing this work was recently accepted for publication in The Astrophysical Journal.
The researchers were able to measure such a small shift because they combined Chandra’s high-resolution images with a careful technique of checking the coordinates of the pulsar and other X-ray sources using precise positions from the Gaia satellite. European Space Agency.
Xi and his team’s latest work on G292.0+1.8 was presented at the 240th meeting of the American Astronomical Society in Pasadena, California. The results are also discussed in an article which has been accepted into the ApJ and is available online.
NASA’s Marshall Space Flight Center manages the Chandra program. The Smithsonian Astrophysical Observatory’s Chandra X-ray Center controls science operations from Cambridge, Massachusetts, and flight operations from Burlington, Massachusetts.
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