The universe’s hum and an opportunity to explore
Present circumstances:
- The background “hum” of nanohertz gravity waves, which have long been theorised to be ubiquitous ultra-low frequency ripples in spacetime emanating from various sources continuously all around us, has now been convincingly demonstrated by physicists for the first time.
- International collaboration was used to achieve the results, with a special thanks to the teams working on the Indo-Japanese Pulsar Timing Array (InPTA) using the GMRT telescope close to Pune.
Historic Context:
- The first gravitational wave finding was announced on February 11, 2016. Almost exactly a century ago, Albert Einstein foresaw this as a logical outcome of his theory of gravity, the Theory of General Relativity.
- In accordance with General Relativity, certain circumstances would cause space to be stretched and compressed, resulting in gravitational waves. This is like to throwing a stone into motionless water.
Impact of gravitational waves:
- Since then, the discovery and investigation of gravitational waves have provided a new window into our world at the largest scales.
- Due to this, astronomers engaged in a number of collaborative projects have announced the finding of ultra-low frequency gravitational waves, which may open up new opportunities for investigating as-yet unexplored cosmic regions.
- Gravitational waves were discovered by LIGO (Laser Interferometry Gravitational-wave Observatory).
- The interference principle serves as the foundation for LIGO, as suggested by its name.
- Two distinct laser beams are sent down parallel pairs of arms, each many km long, that are perpendicular to the other. After being reflected back, the rays are designed to interfere.
- The beams precisely cancel one another out in the absence of any interference.
- The interferometer arms will, on rare occasions, be stretched and contracted by a minute amount million trillion times smaller than the proton as a result of a gravitational wave passing through them.
- This will prohibit the beams from cancelling each other. Before the signal is confirmed as a gravitational wave detection, deep data processing is used to rule out alternatives like seismic vibrations.
- Since the discovery of gravitational waves, numerous brief, high-frequency gravitational wave bursts have been observed by the LIGO (Laser Interferometry Gravitational-wave Observatory) detectors.
- These high-frequency waves are thought to be the result of neutron stars and black holes colliding; each of these objects is around the size of our sun. Black holes and neutron stars are the stellar byproducts of stars that have run out of nuclear fuel.
LISA (Laser Interferometer Space Antenna) is a step ahead of LIGO:
- All of the LIGO and other detectors’ detections have involved high-frequency waves, which typically have a frequency of several kilohertz. The detector’s arms’ length controls its sensitivity; the longer the arms, the more sensitive it is to waves of lower frequency.
- This is one of the motivating factors for LISA, the proposed space-based detector from the European Space Agency. Millions of kilometres would be covered by the detector’s arms.
- To detect the already detected nanohertz waves (one billionth of a hertz), one would have needed a detector the size of a galaxy, which is not buildable.
The elusive waves are located using radio pulses:
- The main idea is to use radio pulses from objects known as millisecond pulsars to discover the elusive waves. Millisecond pulsars are neutron stars that rotate quickly and periodically release radio waves.
- Amazingly frequently, the planet is struck by these pulses. If an ultra-low frequency gravitational wave disturbs the area between a pulsar and us, the arrival time of these pulses may change.
- Years of rigorous data collection from numerous millisecond pulsars are required. For more than 20 years, five worldwide teams have been gathering data on pulsar timings for this reason.
- These include the North American Nanohertz Observatory for Gravitational Waves, the Parkes PTA from Australia, the Chinese Pulsar Timing Array, the Indo-Japanese Pulsar Timing Array, and the European Pulsar Timing Array (PTA).
India-Japan coloration for detecting low frequency waves:
- Data was collected utilising the upgraded Giant Metre wave Radio Telescope (GMRT) at Narayangaon, close to Pune, by members of the Indo-Japan PTA from the National Centre for Radio Astrophysics (NCRA), the Raman Research Institute, and many other institutions.
- The world’s most advanced radio telescope for low-frequency research is this array of 30 radio antennae, each with a diameter of 45 metres. The distance between the antennae is capped at 25 km.
- Data from a particular class of millisecond pulsars were acquired for more than 10 years in order to determine the influence of gravitational waves.
Current barriers to the detection of gravitational waves:
- Numerous factors may affect the timing of the pulsars. These all require separate tracking down and payment.
- Such a tiny signal can only be separated from the noise by statistical analysis of multiple pulsars over a long period of time.
- This is one of the reasons no group has ever asserted that it has discovered a discovery that is infallible, or at the five-sigma level, in scientific jargon, where the probability of a random occurrence occurring is one part in 3.5 million.
- But everyone agrees that when more data is gathered and processed, the gold standard will eventually be reached.
Generating and detecting nanohertz waves:
- The cause of these nanohertz vibrations has not yet been established, despite the fact that the most plausible scenario includes supermassive black holes orbiting one another.
- At the galactic centre, blackholes, which have masses millions of times bigger than that of the Sun, are commonly discovered. When galaxies collide or merge, these may pair off and produce the waves that are observed.
- These space-time alterations are caused by the interaction of mergers and collisions, which creates their background.
- The existence of unusual phenomena like cosmic strings or even inflation, an event that occurred at the very beginning of the universe and led it to expand exponentially, are among the other possibilities that are being investigated.
Conclusion:
- It should be clear that in the future, these nanohertz waves will make it possible for us to research the early universe.
- If the “hum” is the original “aum,” as one critic seems to think, we can only wait and see. Or, hear.
