Every 4 milliseconds, a dead star shoots a powerful beam of radiation at our planet. Do not worry – Earth will be alright. It’s the dead star’s tiny companion that’s in trouble.
In a new study published in the Preprint database on March 11 arXiv (opens in new tab)researchers describe this ill-fated binary star system – a rare class of celestial objects known as a Black widow pulsar (opens in new tab). Just like the cannibal spider that gives this type of system its name, the larger member of the pair seems intent on devouring and destroying its smaller companion. (In spiders, females are often larger than males.)
However, there will be no quick decapitation for this black widow; the larger star seems to kill its partner much more slowly. Over hundreds or thousands of years, the larger star sucked in matter from the smaller star’s vicinity while simultaneously bombarding the smaller star with flashing beams of energy, blasting even more matter into space.
One day it’s possible that the larger star will completely engulf the smaller one, the study’s lead author Emma van der Wateren, a PhD student at the Netherlands Institute for Radio Astronomy (ASTRON), told Live Science. But until then, scientists hope to get this strange system working. By monitoring the larger star’s remarkably steady pulses for sudden irregularities, the study’s authors hope this pulsar could help them spot rare ripples in the tissue of leisure (opens in new tab) known as gravitational waves.
“To detect gravitational waves, you need many, many very stable pulsars,” said van der Wateren. “And unlike previously discovered black widow pulsars, this system is very stable.”
Scientists discovered the star system J0610-2100 about 10,000 light-years from Earth in 2003 when they observed its periodic pulsation with a radio telescope. The researchers thought the system was a pulsar – a type of small, dense, collapsed star that is rotating extremely rapidly.
These dead stars are highly magnetized and shoot out electromagnetic beams from their poles as they spin. When one of these rays is pointing towards the earth, the effect is like a lighthouse, with the light flicking on and off as the ray flashes past us. If the light blinks once every 10 milliseconds or less (like J0610−2100, which blinks every 3.8 milliseconds), then the star fits into an even rarer category called a millisecond pulsar.
Many millisecond pulsars share their orbits with sun-like companion stars that are slowly consuming the pulsars. As the pulsars engulf the companion star’s spinning disks of material, they glow in X-rays seen across the galaxy.
And sometimes a pulsar can drain more than its fair share of matter from its companion. When a pulsar’s companion star has a mass less than a tenth of Earth’s mass, that star system is known as a Black Widow pulsar.
J0610−2100 was the third black widow pulsar ever discovered – and appears to be one of the hungriest. The pulsar’s companion star measures just 0.02 solar masses and completes an orbit around the pulsar about every seven hours, according to the study.
For their new work, van der Wateren and her colleagues analyzed 16 years of radio telescope data from this cannibal star system. Although the system is unmistakably a Black Widow pulsar, the team was surprised to find that it lacked some distinctive quirks.
For example, the star system has never exhibited what is known as a radio eclipse—an almost universal phenomenon in other black widow pulsars.
“Usually, the pulsar’s radio emissions disappear completely for part of the binary orbit,” said van der Wateren. “This happens when the companion star moves close to the front of the pulsar and all this irradiated material coming from the companion eclipses the pulsar’s pulse emission.”
For 16 years, the star system also never showed any temporal anomalies — sudden, tiny differences in the timing of a pulsar compared to astronomers’ predictions.
waves that move the universe
The absence of these two common phenomena is difficult to explain, van der Wateren said. It could be that the line of sight on this pulsar is distorted so that radio eclipses are simply not visible to ground-based telescopes, or perhaps the pulsar’s companion star is not quite as illuminated as other known pulsars that exhibit these features. But whatever the case, this black widow system is incredibly stable and predictable — making it a perfect candidate for gravitational-wave detection, the researchers said.
These waves (first predicted by Albert Einstein) occur when the most massive objects in the universe interact—such as black holes or neutron stars collide. The waves ripple through time and space at the speed of light, distorting the fabric of the universe as they pass.
One way astronomers are hoping to detect gravitational waves is to monitor dozens of millisecond pulsars simultaneously, using systems called pulsar timing arrays. If every pulsar in the array suddenly experiences a timing irregularity around the same time, it could be an indication that something massive, like a gravitational wave, has disrupted their pulses on their way to Earth.
“We have not yet detected gravitational waves in this way,” said van der Wateren. “But I think we’re getting closer.
That’s what makes the discovery of highly predictable black widow pulsars like this so important, van der Wateren added.
Because of their radio eclipses and timing inconsistencies, black widow pulsars are usually too temperamental and rarely good candidates for gravitational-wave detection. But J0610−2100 might be an exception – and its very existence suggests that there might be other suitable exceptions as well. Like the arachnid namesake, this black widow’s cannibal bite may end up serving a greater purpose.
Originally published on Live Science.