Merging black holes emit gravitational waves. However, the waves detected by LIGO are from black
holes, which are a few tens of times heavier than the sun, and that experiment cannot detect these very large wavelengths, low-frequency gravitational waves. These waves have lengths spanning many lightyears. An attempt has been made by the researchers at the IIT-Hyderabad, to catch them using an extraordinary technique.
“In the early universe, we expect to see a lot of gigantic galaxies, with supermassive black holes many billion times the mass of our Sun. We expect that when these galaxies merge, these black holes also eventually merge. As it was confirmed in the Nobel Prize-winning discovery by the LIGO collaboration in 2017 (discovery in 2015),” informs the authorised official from IIT- Hyderabad.
The research team led by Prof Shantanu Desai, Department of Physics, IIT, Hyderabad, comprising Aman Srivastava, a PhD student; Divyansh Kharbanda, a B.Tech student; and Raghav Girgaonkar, an anIIT-Hyderabad alumnus, has recently published a paper based on the first official data from the Indian Pulsar Timing Array (InPTA), in a journal published by the Astronomical Society of Australia.
“Project’s primary aim was to make this data available to our international collaborators, to eventually lead to a data combination which would pave the way to the detection of nanohertz gravitational waves,” an IIT-Hyderabad official informs India Science Wire.
Pulsars are compact stars whose radio signals can be detected quite regularly as pulsations, allowing researchers to use them like clock ticks. As gravitational waves squeeze and stretch space and time as they pass by, the time of arrival of these pulses to earth changes. By regularly monitoring these pulsars for these changes in their time of arrival, researchers hope to detect these gravitational waves from supermassive black holes and gain insight into the early universe.
Researchers at the Indian Pulsar Timing Array (InPTA) have been observing a set of pulsars using the giant metre-wave radio telescope near Pune to aid in the global effort to detect these gravitational waves.
The space between the Earth and the pulsars is not entirely empty. A certain density of electrons and protons can be found inhabiting this space. The variation in this density varies, therefore, this is a kind of interstellar weather. Its presence affects observations and taking the phenomena caused by this column of particles into account, we can use pulsars as clocks better.
“InPTA has the most accurate measurement of this ‘Dispersion Measure’ of all currently operating Pulsar Timing Array (PTA),” says the official while explaining the significance of the study.
More number of PTAs combining their data, especially the current one providing important insights into the said interstellar weather’, will lead to the faster detection of the gravitational waves, which will eventually let the researchers probe into the mystery of how and when these supermassive black holes were formed. The output of this study is being combined and used in multiple international projects to do the same.
The precise knowledge of how ‘interstellar weather’ changes with time, can help us understand the phenomena happening between the Earth and the pulsar.
“Pulsars were traditionally used as clocks using a well-tested ‘narrowband’ method. Recently, another independent process to obtain the same results was proposed, usually referred to as the ‘wideband’ method. We obtained our results using both and found them to agree with each other. We have also demonstrated that low-frequency observations of pulsars can produce competitive results,” an IIT-Hyderabad official explains.
The researchers used uGMRT, a radio telescope made up of 30 dishes, to observe pulsars simultaneously at two different frequencies. Like how red and blue lights have different frequencies, helping us distinguish between objects and their properties, observing pulsars at two different frequencies together helps glean unique properties of the star and the medium between Earth and the pulsar.
“We are the only PTA that carries out observations in this unique manner,” claims an IIT Hyderabad official.
The researchers hope to see more such simultaneous multi-frequency observations of pulsars being carried out by future observatories, such as the Square Kilometre Array, which will be the largest radio telescope ever built. They have also recommended the unrestricted use of the now public dataset for low-frequency pulsar studies. (India Science Wire)
