ASTRON: Super star takes on black holes in jet contest

4 August 2015

In a study published today, a team of scientists in the Netherlands and Australia discovered powerful jets blasting out of a double star system known as PSR J1023+0038. ASTRON astronomer Adam Deller led the research. ASTRON is a division of NWO. It was previously thought that the only objects in the Universe capable of forming such powerful jets were black holes. Now research suggests a super-dense star formed in the aftermath of a supernova explosion is shooting out powerful jets of material into space as well.

A model of the 'super star'. Credit: ICRAR

PSR J1023+0038 contains an extremely dense type of star astronomers call a neutron star, in a close orbit with another, more normal star nearby. It was first identified as a neutron star in 2009 by ASTRON astronomer and Veni laureate, Anne Archibald but it was only when the research team observed the star with the Karl G. Jansky Very Large Array radio telescope in the United States in 2013 and 2014 that they realised the star was producing much stronger jets than expected.

ASTRON astronomer Adam Deller, who led the research, says neutron stars and black holes are sometimes found in orbit with a nearby “companion” star.

“Gas can then flow from the companion star to the neutron star or black hole, producing spectacular displays when some of the material is blasted out in powerful jets at close to the speed of light,” he says. “From what we had seen previously, black holes were the undisputed kings of forming powerful jets, even when they were only fed by a little bit of material from their companion star.

In comparison, neutron stars seemed to make relatively puny jets, which only became bright enough to see when the neutron star was gobbling gas from their companion at a very high rate.”

Dr Deller says when the team looked at PSR J1023+0038 it was only consuming a trickle of material and should have been producing a very feeble jet. “But our observations suggest its jets are nearly as strong as you’d expect from a black hole,” he says.

Astronomer James Miller-Jones, from the International Centre for Radio Astronomy Research (ICRAR), says neutron stars can be thought of as stellar corpses. “They’re formed when a massive star runs out of fuel and undergoes a supernova, and the central parts of the star collapse under their own gravity,” he says. “These things are typically about one and a half times the mass of the Sun and yet they’re only 10-15km across, so they’re incredibly dense.”

Dr Miller-Jones says PSR J1023+0038 is a “transitional” neutron star, spending years at a time powered mainly by the rotation of the neutron star but transitioning occasionally into an active gathering state, when it gets much brighter. “Two other transitional systems are now known and both of these have also been shown to exhibit powerful jets,” he says. “This is casting neutron stars in a new light and showing that in fact they can sometimes launch jets to rival those coming from black holes.”

The ASTRON and JIVE scientists involved in this research were Adam Deller, Javier Moldon, Jason Hessels, Anne Archibald, Zsolt Paragi, George Heald, and Nicolas Vilchez.

The research was published today in the Astrophysical Journal, Volume 809, Issue 1. 


Image

An artist's impression of the binary star system PSR J1023+0038. The extremely dense, rapidly-spinning neutron star, just 10-15 km in size, is in a close orbit with a more normal companion star. The strong gravity of the neutron star pulls gas from its companion, which spirals in towards the neutron star, forming a disk. Some fraction of that gas gets accelerated outwards in energetic, oppositely-directed jets, which give off the radio waves that can be seen by Earth’s radio telescopes. Credit: ICRAR.

Source: ASTRON Netherlands Institute for Radio Astronomy