Artists impression of one prospective source of continuous gravitational waves– Asymmetric accretion onto a spinning neutron star. Credit: Mark Myers, Ozgrav-Swinburne University
In the last couple of years, astronomers have attained an extraordinary turning point: the detection of gravitational waves, vanishingly weak ripples in the material of area and time originating from a few of the most catastrophic events in deep space, consisting of crashes between black holes and neutron stars. So far there have actually been over 90 gravitational-wave detections of such events, observable for only ~ 0.1 to 100 seconds. There may be other sources of gravitational waves, and astronomers are still on the hunt for constant gravitational waves
Continuous gravitational waves ought to be easier to find because they are much longer in duration compared to signals from compact-object accidents. A possible source of constant waves is neutron stars, which are outstanding “corpses” left over from supernova explosions of enormous stars. After the preliminary explosion, the star collapses in on itself, crushing atoms down into a super-dense ball of subatomic particles called “neutrons”– hence the name “neutron star.” The continuous wave signal is related to how fast the neutron star is spinning, so exact measurements of the spin frequency utilizing more conventional telescopes would considerably enhance the possibility of detection of these elusive waves.
In a recent study, led by OzGrav PhD student Shanika Galaudage from Monash University, scientists aimed to figure out neutron stars spin frequencies to assist find constant gravitational waves.
Possible sources of constant gravitational waves.
In this study, researchers hypothesized that continuous gravitational-waves indirectly originate from the gradual accumulation of matter onto a neutron star from a low-mass companion star– these binary systems of a neutron star and buddy star are called low-mass X-ray binaries (LMXBs).
If the neutron star can preserve a built up “mountain” of matter, (even if just a couple of centimeters in height!), it will produce constant waves. The frequency of these waves relate to how quickly the neutron star is spinning. The faster you collect this matter, the bigger the “mountain,” producing bigger continuous waves. Systems that accumulate this matter more quickly are also brighter in X-ray light. Therefore the brightest LMXBs are the most appealing targets for identifying continuous waves.
Scorpius X-1 (Sco X-1) and Cygnus X-1 (Cyg X-2) are two of the brightest LMXB systems– Sco X-1 ranks 2nd in X-ray brightness compared to the Sun. In addition to their severe brightness, scientists know a lot about these 2 LMXB systems, making them ideal sources of continuous waves to study. Their spin frequencies are still unknown.
” A method we can identify how fast these neutron stars are spinning is by searching for X-ray pulsations,” states study lead Shanika Galaudage. “X-ray pulsations from neutron stars are like cosmic lighthouses. If we can time the pulse we would instantly have the ability to reveal their spin frequency and get closer to spotting the continuous gravitational-wave signal.”
” Sco X-1 is among the best prospects we have for making a first detection of continuous gravitational waves, but its an extremely difficult data analysis issue,” states OzGrav scientist and research study co-author Karl Wette, from The Australian National University. “Finding a spin frequency in the X-ray information would be like shining a spotlight on the gravitational wave data: here, this is where we must be looking. Sco X-1 would then be a red-hot preferred to detect continuous gravitational waves.”
Searching for X-ray pulsations
The team carried out a search for X-ray pulsations from Sco X-1 and Cyg X-2. They processed over 1000 hours of X-ray data collected by the Rossi X-ray Timing Explorer instrument. The search used a total of ~ 500 hours of computational time on the OzSTAR supercomputer!
The study did not discover any clear evidence of pulsations from these LMXB sources. In the case of Sco X-1, it might possibly be a black hole, which we would not expect to produce X-ray pulsations.
The research study does find the very best limits on how intense these X-ray pulsations might be if they did take place; these outcomes might imply that neutron stars can not sustain mountains of matter under their strong gravity. Future research study can build on this research study by using much better search methods and more delicate information.
Written by OzGrav researcher Shanika Galaudage (Monash University).
In the last couple of years, astronomers have achieved an extraordinary milestone: the detection of gravitational waves, vanishingly weak ripples in the fabric of space and time emanating from some of the most cataclysmic events in the Universe, including collisions in between black holes and neutron stars. There may be other sources of gravitational waves, and astronomers are still on the hunt for constant gravitational waves
A possible source of continuous waves is neutron stars, which are excellent “remains” left over from supernova explosions of huge stars. The continuous wave signal is related to how quick the neutron star is spinning, so exact measurements of the spin frequency using more standard telescopes would considerably enhance the possibility of detection of these elusive waves.
The frequency of these waves relate to how fast the neutron star is spinning.
