Left: A 14-billion-year long timeline of the universe (left) from the Big Bang to the appearance of fluctuations and the formation of galaxies. Right: Panels showing the structure of the universe today at different resolutions. Image by European Space Agency (ESA) – C Carreau.
The public talks began with L Sriramkumar, a Professor of Physics at the Indian Institute of Technology, Madras, speaking about ‘Mapping the Cosmos: General Relativity and the Timeline of the Universe’. The universe has a rather uniform distribution of matter at the largest scale, but it can be “lumpy” at small spatial scales, where stars group to form galaxies, which come together to form galaxy clusters. According to the standard view of cosmology, this heterogeneity arose when the universe originated with the hot Big Bang and expanded, a process that continues until today. A red shift in the electromagnetic spectra of galaxies provides evidence that they are moving away from each other. This is because of spacetime expansion given by the general theory of relativity, much like how dots on an inflating balloon grow in size and move apart.
L Sriramkumar from IIT Madras, spoke about the history of the universe in his talk ‘Mapping the Cosmos: General Relativity and the Timeline of the Universe’. (Photo: IMSc Media)
Apart from galaxies, the universe is permeated by radiation, most of which is in the microwave region of the electromagnetic spectrum. This is a remnant of the high temperatures during the Big Bang, which can give us clues about the early universe. The universe cooled on expansion and the soup of protons and neutrons came together as atoms, allowing radiation to propagate without interacting with matter. However, quantum fluctuations in the early universe resulted in an uneven distribution of temperature, which can be inferred from the cosmic microwave radiation. More precise observations of this background radiation can help us understand processes in the early universe.
Origins of the universe
Improved resolution of the cosmic microwave background detected by three generations of satellites. COBE - Cosmic Background Explorer, WMAP - Wilkinson Microwave Anisotropic Probe. Image by NASA/JPL-Caltech/ESA.
In the following talk, Tarun Souradeep, Director of Raman Research Institute, Bangalore, spoke about ‘Echoes from the beginning: ECHO from the CMB-BHARAT’. The early universe can be described as a soup of radiation, which reaches us from the far reaches of the universe as the cosmic microwave background. Looking at this radiation farther away from us allows us to peer at events going back in time, as much as the universe at half a million years old. Over the last three decades, we have been able to see these past snapshots of the universe at higher definition using generations of space missions and ground-based observations. These studies have revealed that small inconsistencies in the early universe grew by gravitational instability to shape its large-scale structure today.
Tarun Souradeep, Director of the Raman Research Institute, Bangalore, spoke about the history and future of Cosmic Microwave background (CMB) research in his talk titled ‘Echoes from the beginning: ECHO from the CMB-BHARAT’. (Photo: IMSc Media)
Looking ahead, a space-based observation platform can allow us to access a broader range of wavelengths of the cosmic microwave background. High-resolution observations can refine the parameters in the existing cosmological models. More importantly, these observations can help us understand the source and nature of perturbations in the early universe using signatures of the associated gravitational waves (ripples in spacetime). This will help us answer the fundamental question of when and how the universe originated. The CMB-Bharat consortium of researchers has proposed a satellite that can carry out these observations and contribute to “path-breaking, high-value and legacy science” in India.
The first stars are born
A composite image of the planned SKA-Low telescope in Western Australia. Image by SKAO.Tirthankar Roy Choudhury, a professor at the National Centre for Radio Astrophysics-Tata Institute of Fundamental Research, Pune, spoke about probing the birth of galaxies in his talk on ‘From darkness to light: The SKA’s quest through cosmic time’. The early universe was dark before stars started to form, and light emerged in the “cosmic dawn” when the universe was around 200 million years old. Scientists have tried to understand this phase of the universe using observations from telescopes such as the James Webb Space Telescope, which detect signals from bright galaxies. However, a more complete picture of the cosmic dawn needs complementary observations and theoretical models.
Tirthankar Roy Choudhury from NCRA, Pune, gave an overview of efforts to understand the origin of galaxies in his talk ‘From darkness to light: The SKA’s quest through cosmic time’. (Photo: IMSc Media)
When stars form, hydrogen atoms in the intergalactic medium get ionized because of the star’s radiation, with atoms closer to a galaxy changing first. Radiosignals coming from neutral hydrogen atoms can tell us about their distribution relative to the ionized state, providing an indirect signal of star formation. These signals have long wavelengths and can only be captured using really large and sensitive telescopes. One such ambitious inter-governmental project is the Square Kilometre Array (SKA) Observatory, which is building two large arrays of telescopes in Australia and South Africa. India joined the project a decade ago, contributing to software development and hardware prototyping, and formally became a member country last year. Around 24 Indian institutions and working groups are currently contributing to various aspects of the project.
The death of stars
The planned LIGO-India project is a multi-institutional effort that will help in better sky coverage and localization of gravitational waves from binary blackhole mergers. Image by LIGO-India/IUCAA.
The last lecture in the series was by KG Arun, a professor at the Chennai Mathematical Institute, Chennai, who spoke about the final stages of a star’s life in his talk ‘Ripples in spacetime: LIGO and the late universe’. When a massive star dies after exhausting all its fuel, it undergoes a supernova explosion. If it is less than 30 times the mass of a sun, it turns into a neutron star, while a more massive star collapses into a blackhole, where all its mass is compacted to a single point. Around four-fifths of the stars in our galaxy occur as binaries, a pair of stars that revolve around each other. Dancing around each other in the swang song of their life, these dense objects send out ripples in spacetime known as gravitational waves.
KG Arun from CMI, Chennai, spoke about studying the death of stars in his talk titled 'Ripples in spacetime: LIGO and the late universe’. (Photo: IMSc Media)
Gravitational waves can be used to probe parts of the universe that are dark and cannot be detected by telescopes. As accelerating blackhole binaries lose energy, their orbits get smaller and they spiral into each other, sending out gravitational waves with increasing amplitude and frequency, before their final merger. These gravitational waves are really faint by the time they reach the earth and need sensitive instruments for detection. The Laser Interferometer Gravitational-Wave Observatory (LIGO) in the USA is one such detector, which found the first blackhole merger a decade ago. The multi-institutional LIGO-India being built in Maharashtra will help in better localization of the source of gravitational waves and significantly increase the volume of the universe being observed in concert with the other facilities.
