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Context

• NASA's upcoming Nancy Grace Roman Space Telescope is set to embark on a groundbreaking mission: hunting for primordial black holes, which date back billions of years to the Big Bang.
• The mission is scheduled to launch in late 2026, with the aim of challenging our understanding of the universe's early epochs.

Details

• Detecting Earth-mass primordial black holes would revolutionize astronomy and particle physics, as these objects cannot be formed by known physical processes.
• If confirmed, the existence of primordial black holes would challenge our understanding of the universe's early epochs, approximately 13.8 billion years ago.
• The existence of primordial black holes remains speculative, with theories such as Hawking radiation proposing their eventual evaporation.
• Hawking's theory suggests that black holes emit radiation and eventually evaporate, posing a challenge to the survival of primordial black holes over billions of years.

Roman's Detection Strategy

• Gravitational Microlensing: Roman's strategy relies on gravitational microlensing, a phenomenon predicted by Einstein's general relativity, to detect primordial black holes.
• Observational Approach: By monitoring distortions in light caused by massive objects, Roman aims to identify primordial black holes disguised as Earth-mass rogue planets.

About the telescope

• Formerly known as the Wide-Field Infrared Survey Telescope (WFIRST), the Nancy Grace Roman Space Telescope is an upcoming NASA infrared space telescope.
• Named in honor of Nancy Grace Roman, the former NASA Chief of Astronomy, the telescope aims to address fundamental questions in cosmology and exoplanet research.

Telescope Specifications:

• Primary Mirror: Based on an existing 2.4 m wide-field primary mirror.
• Instruments: The telescope will carry two scientific instruments: the Wide-Field Instrument (WFI) and the Coronagraphic Instrument (CGI).

Wide-Field Instrument (WFI):

• Capabilities: A 300.8-megapixel multi-band visible and near-infrared camera.
• Field of View: Provides a sharpness of images over a 0.28 square degree field of view, which is 100 times larger than imaging cameras on the Hubble Space Telescope.
• Scientific Applications: Enables studies of dark energy, gravitational microlensing for exoplanet detection, and survey investigations of the universe.

Coronagraphic Instrument (CGI):

• Functionality: A high-contrast, small field of view camera and spectrometer covering visible and near-infrared wavelengths.
• Technology: Utilizes dual deformable mirror starlight-suppression technology to achieve high contrast and enable the detection and spectroscopy of exoplanets.

Scientific Objectives:

• Dark Energy Studies: Investigates the nature of dark energy through baryon acoustic oscillations, supernovae observations, and weak gravitational lensing.
• Exoplanet Census: Conducts a comprehensive census of exoplanets to assess their abundance and diversity, including the potential for habitability.
• Galactic and Extragalactic Surveys: Establishes a guest investigator mode to facilitate diverse survey investigations of our galaxy and the universe.
• Exoplanet Direct Imaging: Provides a coronagraph for direct imaging of exoplanets, aiming to capture the first direct images and spectra of planets around nearby stars.

About the Big Bang Theory

• The Big Bang Theory is the prevailing cosmological model for the observable universe's earliest known periods.
• It proposes that the universe began as an extremely hot, dense point roughly 13.8 billion years ago and has since been expanding and cooling.

Early Universe Conditions:

• Singularity: The universe originated from a singularity, an infinitely small and dense point where all matter and energy were concentrated.
• Rapid Expansion: This singularity underwent rapid expansion, known as cosmic inflation, leading to the formation of space, time, and matter.

Timeline of Events:

• Planck Epoch: The earliest epoch, where the fundamental forces of gravity, electromagnetism, and the strong and weak nuclear forces were unified.
• Inflationary Epoch: A period of rapid expansion, causing the universe to expand exponentially and smoothing out irregularities.
• Quark Epoch: Protons and neutrons formed, and quarks combined to form atomic nuclei.
• Hadron Epoch: The universe cooled further, allowing protons and neutrons to combine to form hydrogen and helium nuclei.
• Lepton Epoch: Leptons and antileptons dominated the universe, interacting through weak nuclear force.
• Photon Epoch: The universe became transparent as electrons combined with nuclei to form neutral atoms, allowing photons to travel freely.
• Cosmic Microwave Background: Relics from the photon epoch, detected as cosmic microwave background radiation, provide crucial evidence for the Big Bang.

Expansion and Cooling:

• Hubble's Law: Observations show that galaxies are moving away from each other, indicating the expansion of the universe.
• Redshift: The stretching of light wavelengths due to the universe's expansion, observed as a redshift in the spectrum of distant galaxies.
• Cosmic Microwave Background (CMB): Detected in 1965, the CMB is the residual radiation from the early universe's hot, dense state and supports the Big Bang Theory.

Evidence Supporting the Big Bang:

• Cosmic Microwave Background: The CMB provides a snapshot of the universe's early conditions, supporting the Big Bang Theory's predictions.
• Redshift Observations: Distant galaxies exhibit redshift, consistent with the universe's expansion and supporting Hubble's Law.
• Abundance of Light Elements: The observed abundance of light elements in the universe matches predictions made by nucleosynthesis during the Big Bang.

Challenges:

• While inflationary theory addresses some questions, the precise mechanism and initial conditions of inflation remain theoretical challenges.
• The presence of dark matter and dark energy, which constitute the majority of the universe's mass-energy content, pose challenges to our understanding of cosmic evolution.

About Gravitational Microlensing

• Gravitational microlensing is a phenomenon predicted by Einstein's general theory of relativity, where the gravitational field of a massive object (lens) bends and focuses light from a background source, creating a temporary increase in brightness.
• When a massive object passes between an observer and a distant light source, such as a star, its gravitational field acts as a lens, deflecting and magnifying the light rays.
• Microlensing occurs on a small scale, involving compact objects like stars, planets, or black holes, and does not require alignment on the same axis as traditional gravitational lensing.

About Primordial Black Holes

• Primordial black holes (PBHs) are hypothesized to be black holes formed in the early universe shortly after the Big Bang due to gravitational collapse of high-density regions.
• PBHs are theorized to have a wide range of masses, from microscopic to several solar masses, depending on the specific formation mechanism.
• Unlike stellar black holes formed from collapsing massive stars, PBHs are not associated with stellar evolution and can have unique properties.
• Quantum fluctuations during cosmic inflation could also lead to the formation of PBHs, with masses determined by the scale of inflation.

About Relativity

• Albert Einstein formulated two theories of relativity: the Special Theory of Relativity (STR) in 1905 and the General Theory of Relativity (GTR) in 1915.
• Both theories challenge classical notions of space, time, and gravity, offering a new understanding of the universe.

Special Theory of Relativity (STR):

• Principle of Relativity: The laws of physics are the same in all inertial frames of reference.
• Constancy of the Speed of Light: The speed of light in a vacuum is constant and independent of the motion of the observer or the source.
• Time Dilation: Moving clocks appear to run slower relative to stationary observers, as time dilates with increasing velocity.
• Length Contraction: Objects moving at relativistic speeds contract along their direction of motion as observed by a stationary observer.
• Mass-Energy Equivalence: Einstein's famous equation E=mc2E=mc2 demonstrates the equivalence of mass and energy, where EE is energy, mm is mass, and cc is the speed of light.

General Theory of Relativity (GTR):

• Principle of Equivalence: Gravity is indistinguishable from acceleration. In a freely falling reference frame, there is no gravitational force.
• Curvature of Spacetime: Massive objects deform the fabric of spacetime, causing curvature that dictates the motion of objects in their vicinity.
• Geodesic Motion: Objects follow the shortest path (geodesic) in curved spacetime, resulting in the trajectory of planets around stars and the bending of light by massive objects.
• Gravitational Time Dilation: Clocks in strong gravitational fields run slower compared to clocks in weaker fields, as predicted by GTR.
• Black Holes and Singularities: GTR predicts the existence of black holes, regions of spacetime with infinite curvature where gravity is so strong that nothing, not even light, can escape.

Experimental Confirmations:

• Eddington's Solar Eclipse Expedition: Observations during a solar eclipse in 1919 provided the first experimental evidence supporting GTR, demonstrating the deflection of starlight by the Sun's gravitational field.
• Gravitational Redshift: Measurements of the frequency shift of light from distant stars near massive objects confirm the gravitational time dilation predicted by GTR.
• Gravitational Waves: The detection of gravitational waves by LIGO and other observatories directly confirms the existence of gravitational waves, a key prediction of GTR.

Sources:

Wionews

PRACTICE QUESTION Q.  The Big Bang Theory is the most widely accepted explanation for the origin and evolution of the universe, supported by extensive observational evidence. Comment. (150 words)