Astronomy & Space Technology

Terms related to Black Holes

Black Holes:

Black holes are the regions of spacetime where gravity is so strong that nothing, including light and other electromagnetic waves, has enough energy to escape. The boundary of no escape is called the event horizon.
Formation: A black hole forms when a massive star (at least three times the mass of our Sun), exhausts its fuel, explodes in a supernova, and collapses under gravity into an incredibly dense core called a singularity.
Types:
- Stellar Black Hole: Formed by the collapse of a single massive star.
- Intermediate Black Hole: Formed by the collapse of a star having mass between 100 and 1,00,000 times that of our sun.
- Supermassive Black Hole: Masses ranging from millions to billions of times that of the sun, found at the centres of most galaxies.
Black holes are not directly observable with telescopes that detect X-rays, light, or other forms of electromagnetic radiation. However, their presence can be inferred through their effects on surrounding matter and the gravitational waves they produce.
- E.g., If a black hole passes through a cloud of interstellar matter or if a star passes close to a black hole, it will draw matter inward in a process known as accretion. As the attracted matter accelerates and heats up, it emits X-rays and powerful gamma ray bursts that radiate into space. This reflects the presence of black holes.
- Merger of two blackholes produces powerful gravitational waves. The detection of these gravitational waves (through LIGO - Laser Interferometer Gravitational-Wave Observatory) can confirm the existence/ location of the black holes.

Terms related to black hole:

Supernova: Supernovae are incredibly powerful explosions that occur when a massive supergiant star reaches the end of its life (exhausts its fuel). These explosions release an astonishing amount of energy, up to 10^44 joules.

Singularity: The centre of a black hole is a gravitational singularity, a point where the general theory of relativity breaks down, i.e. where its predictions do not apply. A black hole’s great gravitational pull emerges as if from the singularity.
Event Horizon (a point of no return): The event horizon is like a boundary around a black hole (around the singularity). Once anything (matter, energy, light) crosses this boundary, it can not escape unless it travels faster than the speed of light (which is impossible). This means nothing, not even light, can escape the black hole's strong gravity because the speed needed to escape at the event horizon should be greater than the speed of light.

Ergosphere: The Ergosphere is a bigger sphere, outside the event horizon of a black hole, where matter and even light can enter and then return (escape the black hole's gravitational pull), if they are moving fast enough (with speeds comparable to the speed of light).
- Both rotating (Kerr) black holes and non-rotating (Schwarzschild) black holes have an ergosphere. In the case of rotating black holes, the ergosphere is larger and more elongated compared to non-rotating black holes.
- In the Ergosphere, spacetime is dragged along with the rotation of the black hole. It is theoretically possible to extract energy and angular momentum from the ergosphere via the Penrose process. (The Penrose process suggests a way to take energy and spin from the ergosphere of a rotating black hole.)
  - Some scientists have suggested using this possibility to send an object into the ergosphere and allow it to accelerate there along the black hole’s direction of rotation, so that it comes out of the black hole moving faster.
  - This energy ‘gain’ of the object will translate to the black hole losing some angular momentum.
Accretion disc: An accretion disc is a flat, rotating structure of matter (such as gas, dust, or other material) that forms around a black hole. The material in the accretion disc spirals inward due to gravitational attraction of the black hole. As it spirals inward, the material often heats up due to friction and gravitational forces, emitting various forms of electromagnetic radiation, including visible light, X-rays, gamma rays and radio waves.

Spaghettification: Spaghettification refers to the effect of extreme gravitational pressure on any particle or body of matter, in particular, when exposed to the extreme forces of the black hole.

When a particle draws too close to the event horizon, it is stretched into long thin shapes. E.g., If an astronaut falls into the event horizon, as the gravity is inversely proportional to distance, the pull on the falling astronaut’s legs will be substantially greater than the pull on his or her upper torso. Subsequently, stretching him like spaghetti (pasta).

Astronomers spot unusual object that falls within the black hole ‘mass gap’

Context: An object has been detected in the star clusterNGC 1851, whose mass (between 2.09 and 2.71 times the mass of the Sun) falls within the black hole mass gap.

Major Highlights:

Black Hole Mass Gap:

Neutron stars are incredibly dense objects formed from the collapse of massive stars. Their maximum mass is thought to be around 2.2 solar masses.
Black holes are even more massive, the lightest black holes are believed to be around 5 solar masses.
Between these two ranges lies the "mass gap" - a region where no objects have been definitively identified.
At the boundary between neutron stars and black holes there is always the possibility that some new, as yet unknown, astrophysical object might exist.

The Newly Discovered Object:

This object resides in a binary system within the star cluster NGC 1851, roughly 40,000 light-years from Earth.
Its companion is a millisecond pulsar, a rapidly spinning neutron star that emits regular pulses of radio waves.
By studying the pulsar's orbital motion, astronomers have estimated the mass of the unknown object to be between 2.09 and 2.71 solar masses. This places it within the mass gap.

Neutron Stars:

Neutron stars are the incredibly dense remnants of supermassive stars (with masses around 10²⁵ times the mass of the Sun) that have exploded as supernovae.
- They are formed when massive stars undergo supernova explosions at the end of their lifecycle. During the explosion, the outer layers of the star are expelled into space, while the core collapses under its own gravity. The core becomes so dense that protons and electrons combine to form neutrons, hence the name "neutron star." Neutron stars do not have an event horizon.
  - Supernovae are incredibly powerful explosions that occur when a massive supergiant star reaches the end of its life. These explosions release an astonishing amount of energy, up to 10^44 joules.
Neutron stars are about 15-30 kms in diameter and have a mass between 1.4- 2.2 solar masses. They are the densest known stellar objects in the universe, second only to the black holes.
They have breathtakingly high rotation speeds with rotational periods that can be just 0.3 to 12.0 seconds.
They often possess extremely strong magnetic fields, much stronger than those of regular stars. These magnetic fields can give rise to intense radiation emissions, including beams of electromagnetic radiation and particle streams, which are observable as pulsars.

Black Holes:

Black holes are regions of spacetime where gravity is so strong that nothing, including light and other electromagnetic waves, has enough energy to escape. The boundary of no escape is called the event horizon.
- The event horizon is the boundary surrounding a black hole from which it is impossible for matter or energy to escape the black hole's gravitational pull, i.e., the escape velocity at the event horizon is greater than the speed of light.
It is formed when a dying star (leftover core) having more than three times the mass of the Sun undergoes a gravitational collapse, leading to the creation of a black hole.
- Stellar Black Hole: Formed by the collapse of a single massive star.
- Intermediate Black Hole: Masses between 100 and 1,00,000 times that of the sun.
- Supermassive Black Hole: Masses ranging from millions to billions of times that of the sun, found at the centres of most galaxies.
Black holes are not directly observable. However, their presence can be inferred through their effects on surrounding matter and the gravitational waves they produce.

SLIM (Smart Lander for Investigating Moon) Mission by JAXA (Moon Sniper)

Context: The SLIM (Smart Lander for Investigating Moon) mission has established Japan as the fifth country to successfully land a spacecraft on the moon. This milestone was achieved through the deployment of the robotic "Moon Sniper," which is designed for lunar exploration and surface testing. The SLIM Mission is labelled as Moon Sniper.

About SLIM (Smart Lander for Investigating Moon)

SLIM (Smart Lander for Investigating Moon) is a small-scale exploration of JAXA (Japan’s Space Agency) lander.
"SLIM" is a technology demonstrator, and the expertise gained in precision landing and other technologies will be inherited by future missions such as the Martian Moon eXploration (MMX) and lunar polar missions. It is designed for:
Pinpoint landings on the Moon's surface with a landing accuracy of less than 100 metres. SLIM Mission employs ‘Vision based navigation’ technology for its higher landing accuracy.
Reduction in the size and weight of equipment used in Moon landings which will result in more frequent lunar and planetary landings. SLIM Mission employs small, lightweight and high performance chemical propulsion systems and light-weight materials in designing systems such as computers to save on the weight.
Investigation into the Moon's origins through composition analysis of rocks estimated to be derived from the lunar mantle. There is a theory that the moon was formed by a giant impact. In this case, the composition of the moon's mantle, which makes up 90% of the moon, would be similar to that of Earth. SLIM Mission has selected the landing site close to the SHIOLI crater near the "Sea of Nectar" as the landing target site. Olivine mineral is expected to be present at the Shioli crater, expected to be ejected from Moon’s mantle.

Importance of Pinpoint Landing

SLIM Mission employs Vision Based Navigation System for ensuring enhanced landing accuracy.
Most conventional lunar landers land at a distance of several kilometres to tens of kilometres away from the planned landing site. Low landing accuracy.
Over the years, Moon rovers and landers have adequately mapped the surface of the moon. To take the researcher frontier forward, researchers now aim to study specific sites and rocks on the surface of the Moon. This will require pin-point landing.
For high-resolution lunar in-situ observation of individual rocks, it is necessary to land the spacecraft precisely.
Traversing steep slopes and rough terrain on the moon can be made less challenging with precision landing.
Locations with sustainable water resources are limited to a very narrow area on the Moon. To explore such areas precision landing is required.

Landing on sloped surfaces

Since the SLIM Mission plans to land at a site near a crater which has slope of 15 degrees. The SLIM mission will employ and demonstrate capabilities to land at sloped surfaces by employing a unique two-step landing technology.

The landing sequence of SLIM will be conducted as follows:

Benefits of SLIM Mission

Future solar science exploration will demand the level of navigation accuracy that JAXA is seeking through the SLIM mission.
As scientific knowledge builds on the study object, more specific research will be needed. Placing spacecraft with precision facilitates expertise.
Planetary science exploration will additionally call for highly capable equipment for observation.
Downsizing the exploration system can reinforce the instruments to be placed into a locale especially well-suited for its landing mission.

Thirty Metre Telescope

Context: An Indian delegation led by the Secretary of the Department of Science and Technology (DST) visited Mauna Kea, Hawaii, USA and discussed challenges in the progress of the Thirty Meter Telescope (TMT) project and ways to overcome them.

About Thirty Metre Telescope:

TMT is an international project which aims at building a 30-metre diameter telescope at Mauna Kea, Hawaii, USA.
- At the heart of the telescope is the segmented mirror, made up of 492 individual segments, which makes it three times as wide as the world’s largest existing visible-light telescope.
- Precisely aligned, these segments will work as a single reflective surface of 30 m diameter.
  - The larger the mirror, the more light a telescope can collect, which means that it can see farther, fainter objects.
Upon construction, TMT would be one of the world’s most advanced and capable ground-based optical and infrared observatory.
- Wavelength: Optical, near-infrared, and mid-infrared.
Estimated cost: 1.47 billion USD (Base year 2012 USD).
It is a joint effort of an international consortium of scientific organisations and institutions in Canada, China, India, Japan and USA.

Significance:

The telescope would help in the:

Study of exoplanets and whether their atmospheres contain water vapour or methane — the signatures of possible life, and detection of extraterrestrial life.
Study of black holes, evolution of galaxies, dark matter and dark energy.

Why Mauna Kea?

Mauna Kea is a dormant volcano located on Hawaii’s Big Island, USA.
Astronomers favour Mauna Kea because the clean air and limited light pollution at its summit 4,205 metres above sea level make it one of the world’s best locations for studying the skies.
The area was selected in July of 2009 by the board of the Thirty Meter Telescope after a five-year-long campaign.
The project was started in 2014, but was soon halted due to opposition by native Hawaiins who consider Mauna Kea as sacred, and also concerns regarding environmental damage.
- The indigenous people on the island argue that because of the massive size of the facility, the project would further desecrate the summit.
- The mountain has religious significance for native Hawaiians and already houses 12 observatories on the summit.

China launches new satellite for violent cosmic phenomena observation

Context: China made a significant stride in space exploration by launching a revolutionary astronomical satellite, the Einstein Probe (EP), designed in the shape of a lotus. This groundbreaking initiative aims to delve into mysterious transient phenomena in the universe. The Long March-2C carrier rocket lifted off, carrying the EP into its planned orbit.

Technology and design:

The EP utilizes cutting-edge X-ray detection technology.
The lotus-inspired design incorporates 12 ‘petals’ housing wide-field X-ray telescopes (WXT) and two ‘stamens’ containing follow-up X-ray telescopes (FXT).
Together, these components form a space observatory with the primary objective of capturing the initial light emitted during supernova explosions and exploring the nature of transient celestial objects at the outer reaches of the universe.
Designed with a lifespan of five years, the Einstein Probe employs the astronomical time-domain observation method, conducting a high-sensitivity real-time dynamic sky survey in the soft X-ray band.
Launched from the Xichang Satellite Launch Centre in Sichuan Province, the satellite weighs approximately 1.45 tonnes.

Collaborations:

Collaborating in this ambitious space exploration endeavour are the European Space Agency and the Max Planck Institute for Extraterrestrial Physics in Germany, showcasing the global significance of EP's mission.

Homage to Einstein: This tribute reflects Einstein's predictions regarding black holes and gravitational waves in his general relativity theory.

Theory of General Relativity:

General relativity, a component of the broader theory of relativity formulated by the German physicist Albert Einstein, originated in 1916.
It specifically deals with gravity, one of the foundational forces governing the universe.
Given that gravity dictates the behaviour of macroscopic entities, general relativity serves as the theoretical framework for understanding large-scale physical phenomena.
At its core, general relativity emerges from Einstein's principle of equivalence, asserting that on a local scale, it becomes impossible to distinguish between the physical effects attributed to gravity and those resulting from acceleration. This theory treats gravity as a geometric phenomenon arising from the curvature of space-time.
The field equations derived from general relativity provide solutions applicable to diverse physical scenarios, encompassing planetary dynamics, the life cycle of stars, the intricacies of black holes, and the evolution of the universe itself.
The validity of general relativity has been substantiated through experimental verifications, including observations of gravitational lenses, the trajectory of the planet Mercury, time dilation within Earth's gravitational field, and the detection of gravitational waves emanating from merging black holes.

Aims:

Contrary to the serene night sky visible to the human eye, the universe harbours intense celestial activities, such as the demise of supermassive stars, the consumption of stars by black holes, and collisions involving peculiar neutron stars and black holes.
The satellite's comprehensive survey and monitoring of high-energy transient sources, search for concealed black holes, and investigation into their formation and evolution are expected to significantly contribute to our understanding of the universe.
The EP's capability to capture remote and faint transients and bursts is crucial in overcoming the challenges posed by Earth's atmosphere, absorbing X-rays with valuable information.

Global Space Missions in News

Context: The year 2023 marked a significant period for space exploration, with achievements such as NASA's OSIRIS-REx mission successfully retrieving a sample from an asteroid and India's Chandrayaan-3 mission exploring the lunar south pole area.

National Aeronautics and Space Administration (NASA)’s Mission

OSIRIS-REx (Origins, Spectral Interpretation, Resource Identification, and Security-Regolith Explorer) Mission

This Spacecraft travelled to a near-Earth asteroid named Bennu (formerly 1999 RQ36) and collected a sample of rocks and dust from the surface.

Benefit of the Mission

This mission will help scientists investigate how planets formed and how life began, as well as improve our understanding of asteroids that could impact Earth.

Artemis Plan

In The Artemis mission, NASA wants to land the first woman and first person of colour on the Moon.
It will send humans to the moon for the first time since 1972
This will be achieved by collaborating with commercial and international partners and establishing the first long-term presence on the Moon.

Artemis-I

In this NASA sent an uncrewed capsule into orbit around the moon in 2022.

Artemis-II

Artemis II is the first crewed step in this plan.
In this four astronauts are planned to be on board during the 10-day mission.
It will put the astronauts into orbit around the Moon before returning them home.

CLPS (Commercial Lunar Payload Services) Initiative

Under this initiative NASA is working with many companies to deliver science and technology to the lunar surface.

These companies, ranging in size, bid on delivering payloads for NASA.
This includes everything from payload integration and operations, to launching from Earth and landing on the surface of the Moon.

Europa Clipper

This mission will explore one of Jupiter’s largest moons, Europa.

About Europa

Europa is slightly smaller than Earth’s moon and has a surface made of ice.
Beneath this icy surface, Europa likely harbours a saltwater ocean that scientists expect contains over twice as much water as all the Earth's oceans combined.

Objective of the Mission: To investigate whether Europa’s ocean could be a suitable habitat for extraterrestrial life.

Working: By flying past Europa nearly 50 times to study the moon’s icy shell, its surface’s geology and its subsurface ocean.

VIPER (Volatiles Investigating Polar Exploration Rover)

It is a robot the size of a golf cart that NASA will use to explore the moon’s south pole.

This robotic mission is designed to search for volatiles, which are molecules that easily vaporise, like water and carbon dioxide, at lunar temperatures.

Benefit of the Mission

These materials that will be collected in the mission could provide resources for future human exploration on the moon.

About the Robot

The VIPER robot will rely on batteries, heat pipes and radiators throughout its 100-day mission.
It will handle lunar conditions ranging from scorching 224°F (107°C) in daylight to freezing -240°C in shadowed regions.

SIMPLEx (Small, Innovative Missions for PLanetary Exploration)

The objective of these missions is to save costs by tagging along on other launches as what is called a rideshare, or secondary payload.

Few Examples under SIMPLEx

Lunar Trailblazer

Like VIPER, Lunar Trailblazer will look for water on the moon.
VIPER will explore the moon's south pole, studying a specific area, while Lunar Trailblazer will orbit, mapping water molecules and measuring surface temperature.

Prime-1 Mission

The PRIME-1 mission is Lunar Trailblazer’s ride.
PRIME-1 will drill into the moon.
It's a test run for the kind of drill that VIPER will use.

DART (Double Asteroid Redirection Test)

In this mission the Didymos-Dimorphous asteroid system was used to test a planetary defence technique called 'kinetic impact’.
The kinetic impact technique involves smashing something into an object to alter its path.
The force of the impact was so significant that it actually changed Dimorphos's orbit.

This technique could prove useful if humanity ever discovers a potentially hazardous object on a collision course with Earth and needs to redirect it.

Japanese Exploration Agency (JAXA)’s Mission

MMX (Martian Moon eXploration)

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The objective of the mission is to study Mars' moons, Phobos and Deimos.
The primary aim is to identify the origin of Mars' moons, Phobos and Deimos.
Scientists are uncertain if they are captured asteroids or formed from existing debris in Martian orbit.
MMX will also land on Phobos' surface and collect a sample before returning to Earth.

European Space Agency’s Mission

Hera

Hera is a mission by the European Space Agency to visit the Didymos-Dimorphous asteroid system that NASA’s DART mission visited in 2022.
It will study the physical properties of the asteroids.

Square Kilometre Array Project

Context: India is set to get full member status to the Square Kilometer Array. Indian Cabinet has approved Rs 1,250 crore to support the multinational Square Kilometre Array (SKA) project, whose telescope arrays or groups of telescopes will be built in Australia and South Africa.

About Square Kilometre Array Project

SKA is a group of radio telescopes being built in South Africa and Australia in two phases. The first phase is expected to begin operations by 2029.
The radio telescopes will be operating in two different ranges of radio frequency.
- The South-African array will scan for mid-frequency signals, between 350 MHz and 15.4 GHz.
- The Australian telescope will work in the low-frequency range of 50-350 MHz.
Once constructed, the SKA will be the most powerful radio telescope ever built, capable of detecting faint radio signals from extreme distances, with eventually over a square kilometre (one million square metres) of collecting area.

Objectives

SKA will observe and map galaxies at the edge of the observable universe and the Milky Way in great detail. It will study magnetism and radiation from distant galaxies and map them as well.
- Since the Milky Way galaxy’s view is better from the Southern Hemisphere, the arrays are being constructed there.
Survey data from SKA observation will:
- Provide deep insights about formation and evolution of our galaxy.
- Detect and understand the role of dark matter and dark energy in the universe.
- Aid in the search for life beyond the Earth by looking for planets that orbit stars in habitable zones and studying their atmosphere for organic compounds, as a part of a science programme called Cradle of Life.

Collaborative efforts

It will also be one of the world’s largest collaborative research projects, involving thousands of researchers and the world’s fastest supercomputers.
- Square Kilometre Array Observatory: Founded in 2019, the Square Kilometre Array Observatory (SKAO) has 16 consortium members — Australia, South Africa, Canada, China, India, Japan, South Korea, the UK, Spain, Portugal, Switzerland, France, Germany, the Netherlands, Sweden, and Italy. Headquarters: Jodrell Bank Observatory in the UK.
- The Indian research partner for the SKA project is Pune’s Giant Metrewave Radio Telescope, operated by the National Centre for Radio Astrophysics (NCRA) of Tata Institute of Fundamental Research (TIFR). India’s main contribution to the SKA is in the development, and operation, of the Telescope Manager element, the “neural network” or the software that will make the telescope work.
To improve the accuracy of triangulation of data and its resolution, the project will include additional dishes in the future (phase 2) in neighbouring African countries — Botswana, Ghana, Kenya, Madagascar, Mauritius, Mozambique, Namibia, and Zambia.

Significance for India:

SKA offers opportunities similar to the Large Hadron Collider (LHC) or the ITER, which too are located on foreign soil but have brought rich dividends to the Indian scientific community.
A full member status would provide India preferential access to the SKA facilities. Most existing telescopes operate under an open-use policy which allows research groups from any country to get time on the facility through competitive bidding by making a scientific case.
Member countries will get preferential allocation of time on the radio telescope, roughly in proportion to their contribution to the project, and only limited time slots would be available through competitive bidding.
The Indian participation in SKA led by a consortium of more than 20 academic and research institutes (with NCRA-TIFR as the nodal institute).
During the design phase of the SKA (2014-2020), India has contributed actively to the project, with a lead role in the successful design of the complex Telescope Manager system.
India’s membership in SKAO will enable the large-scale participation of Indian industry not only for fulfilling our commitments towards in-kind contributions but also in other open tenders that may be floated by the SKAO.
Participation in this project will open up possibilities for development of niche skills in Indian industry and research organizations in different areas of next generation technologies, such as modern antenna design, sophisticated cryogenic receiver systems, and high volume optical fibre data transport technology etc.

How Global Positioning System (GPS) work?

GPS, which stands for Global Positioning System, is a satellite-based navigation system.

It is a network of satellites and receiving devices that allows users to determine their precise location (in latitude, longitude, and altitude) and obtain accurate time information anywhere on Earth.

The original GPS system began as a project of the U.S. military. The first experimental satellite for it was launched in 1978.

Components of GPS system:

The GPS system consists of three main components: satellites, ground control stations, and GPS receivers.

Satellites: The space segment consists of 24 satellites which orbit 20,200 km above the earth. These satellites constantly transmit radio signals that contain information about their location, time, and other data. The satellites are arranged in such a way that at least four of them are visible from any point on the Earth's surface at any given time.
Ground Control Stations: The ground control stations are responsible for monitoring and controlling the GPS satellites. They ensure that the satellites are functioning correctly and maintain their precise orbits.
GPS Receivers: GPS receivers are the devices used by users to receive signals from the GPS satellites. These receivers are commonly found in smartphones, navigation devices, and other GPS-enabled devices. The receiver uses a process called trilateration to determine the user's location.

How does GPS work?

The GPS receiver picks up signals from multiple GPS satellites that are in view of the receiver's location.
Each satellite sends out radio signals at the speed of light that includes information about the satellite's location and the precise time the signal was transmitted.
The GPS receiver measures the time it takes for the signals to reach it from each satellite.
Using the known locations of the satellites and the time it took for the signals to travel, the GPS receiver can calculate the distance between itself and each satellite.
With the distance measurements from at least four satellites, the GPS receiver can determine the precise three-dimensional position (latitude, longitude, and altitude) using a process called trilateration.
The GPS receiver can also provide additional information such as speed, direction, and time by continuously updating its position based on the signals received from the satellites.

Why multiple satellites (Trilateration)?

Using multiple satellites makes the GPS data more accurate. If a GPS receiver calculates its distance from only one satellite, it could be that exact distance from the satellite in any direction.
Think of the satellite as a flashlight. When you shine it on the ground, you get a circle of light. With one satellite, the GPS receiver could be anywhere in that circle of light. With two more satellites, there are two more circles. These three circles intersect, or cross, in only one place. That is the location of the GPS receiver. This method of determining location is called trilateration.

Satellite navigation systems of other countries:

Presently, there are four global satellite-based navigation systems.
- United States: Global Position System (GPS)
- Russia: Global Navigation Satellite System (GLONASS)
- China: BeiDou Navigation Satellite System (BDS)
- European Union: Galileo
Japan has a four-satellite regional navigation system (Quasi-Zenith Satellite System).
India has its own Indian Regional Navigation Satellite System NavIC (Navigation with Indian Constellation). Its space segment consists of seven satellites: three in geostationary orbits and four in geosynchronous orbits.

Applications:

Terrestrial, aerial, and marine navigation E.g., Location-based services in mobile devices, visual and voice navigation for drivers.
Vehicle tracking and supply chain management
Mapping, survey and geodetic measurements E.g., mapping of terrains, creating digital maps, and conducting land surveys
Terrestrial navigation aid for hikers and travellers
Disaster management
Precision agriculture E.g., yield monitoring, variable rate application of fertilisers and pesticides.
Meteorology E.g., GPS receivers on weather balloons and satellites provide data on atmospheric conditions to monitor and predict weather patterns more accurately.
Seismology- To monitor ground movements and tectonic plate activity. E.g., GPS stations can detect and measure ground displacements, aiding in earthquake research and early warning systems.
Military Operations- GPS for navigation, target tracking, and coordination of operations.

X-Ray Polarimeter Satellite (XPoSat)

Context: Indian Space Research Organisation (ISRO) has announced that India is set to launch its first X-ray Polarimeter Satellite (XPoSat) onboard the Polar Satellite Launch Vehicle (PSLV) scheduled to be launched in December 2023.

X-Ray Polarimeter Satellite:

XPoSat is India’s first dedicated polarimetry mission to study the polarisation of cosmic X-rays and various dynamics of bright astronomical X-ray sources under extreme conditions.
The spacecraft is designated for observation from Low Earth Orbit (non-sun synchronous orbit of ~650 km altitude, low inclination of ~6 degree).
XPoSat is the world’s second polarimetry mission using X-Ray. NASA’s Imaging X-ray Polarimetry Explorer (IXPE) Mission is the first satellite mission dedicated to measuring the polarisation of X-Rays from different cosmic sources.
The lifespan of the mission is 5 years.

Payloads:

The spacecraft will carry two scientific payloads – an X-Ray Polarimeter (POLIX) and X-ray SPECtroscopy and Timing (XSPECT).
- POLIX: The primary payload, POLIX (Polarimeter Instrument in X-rays), is designed to measure polarimetry parameters, specifically the degree and angle of polarisation, in the medium X-ray energy range of 8-30 keV photons originating from astronomical sources. The payload is developed by the Raman Research Institute, Bengaluru.
- XSPECT: The payload will provide spectroscopic information within the energy range of 0.8-15 keV. The payload is developed by the U.R. Rao Satellite Centre, ISRO. It would observe several types of sources viz. X-ray pulsars, blackhole binaries, low-magnetic field neutron stars in low-mass X-ray binaries, Active galactic nuclei and Magnetars.

Polarisation of light:

Light travels in the form of transverse electromagnetic waves. The light emitted by sources like the sun, bulb, candle etc. has vibrations in several planes (oscillates in all directions), and it is called unpolarised light.
Polarisation is the phenomenon of restricting the vibration of light waves to one specific direction/plane. E.g., Polarised sunglasses have a special filter that allows only light with a specific polarisation direction to pass through, which helps to reduce glare and improve visibility by blocking unwanted polarisations.

Polarimetry:

Polarimetry is a technique to measure the polarisation of light. Polarimetry allows astronomers to observe and measure characteristics of objects, which include:
- Size, shape and orientation of dust particles, such as those surrounding comets or in planet-forming discs around stars.
- Light from faint sources, such as exoplanets or hidden galactic nuclei.
- Scattering properties of light-reflecting bodies (such as planetary atmospheres and the surfaces of rocky bodies).
- Three-dimensional shapes of objects, such as supernovae.
- Magnetic fields around stars and other objects, such as black holes.

Why X-rays?

X-rays are high-frequency and high-energyelectromagnetic radiation and have much shorter wavelengths (ranging from 0.01 to 10 nanometres). X-rays come from objects that are millions of degrees Celsius—such as pulsars, galactic supernovae remnants, and the accretion disk of black holes.
- Since the physical temperature of an object determines the wavelength of the radiation it emits, so the hotter the object, the shorter the wavelength of peak emission.
Since X-rays have very short wavelengths and high energies, so they can penetrate most materials, including the mirrors in telescopes. Hence, scientists use this data collected by X-ray detectors on satellites in orbit around the Earth to see and record the energy flows within the celestial sources.
- From space, X-ray telescopes collect photons from a given region of the sky.
- The photons are directed onto the detector where they are absorbed, and the energy, time, and direction of individual photons are recorded.
- Such measurements can provide clues about the composition, temperature, and density of distant celestial environments.

Significance of the mission:

By measuring the polarisation of X-rays, astronomers can better understand the geometry, composition and physical processes responsible for X-ray emission/production in a variety of astrophysical sources to gain insight into their inner dynamics (like emission mechanisms of celestial objects). It can also shed light on the structure and dynamics of compact objects, such as black holes and neutron stars.
- Astronomical sources, including black holes, neutron stars, active galactic nuclei, and pulsar wind nebulae, have extremely strong gravitational fields and emit X-rays as matter accretes onto them or as they interact with surrounding material. They present complex emission mechanisms that challenge their present scientific understanding.
- By combining polarimetric observations along with spectroscopic and timing measurements, researchers can overcome the limitations of the present understanding of astronomical emission processes.
Measuring X-ray polarisation helps in deducing the orientation and strength of magnetic fields in celestial objects.
- Magnetic fields play a crucial role in many astrophysical processes, including the generation and acceleration of charged particles and the formation of energetic jets and outflows.
X-ray polarisation measurements can help scientists understand the behaviour of high-energy particles in extreme environments.
- X-rays are produced in regions with extreme conditions, such as supernova remnants, active galactic nuclei, and gamma-ray bursts.
- By analysing the polarisation of X-rays from these sources, scientists can gain insights into the mechanisms responsible for particle acceleration, energy transfer, and radiation processes in these energetic phenomena.

Aurora Borealis

Auroras:

Auroras are a natural light display in the sky, predominantly seen in the high-latitude regions (around the Arctic and Antarctic).
- It is called aurora borealis or northern lights near the North Pole.
- It is called aurora australis or southern lights near the South Pole.
Cause: It is caused by the interaction of charged particles from the sun with the Earth's atmosphere.
Aurora borealis is typically seen as a faint glow in the sky, but it can sometimes be very bright and colourful.

What makes this happen?

Apart from heat and light, the Sun also releases energetic charged particles. The protective magnetic field around Earth shields us from most of the energy and particles.
However, the Sun does not send the same amount of energy all the time. There is a constant streaming solar wind and there are also solar storms.
During one kind of solar storm called a coronal mass ejection, the Sun ejects a huge bubble of electrified gas that can travel through space at high speeds.
When a solar storm comes toward Earth, some of the energy and small particles can travel down the magnetic field lines at the north and south poles and enter into the Earth's atmosphere.
There, the particles interact with gases in Earth’s atmosphere and result in beautiful displays of light in the sky.
- Oxygen gives off green and red light.
- Nitrogen glows blue and purple.

Do other planets get auroras?

Auroras do not just happen on Earth. If a planet has an atmosphere and magnetic field, they probably have auroras.
Incredible images of auroras have also been captured on Jupiter, Saturn, Uranus and Neptune.

Gamma-Ray Bursts: Explained

What are Gamma-ray Bursts?

Gamma-ray Bursts (GRBs) are extremely energetic explosions that produce intense flashes of gamma rays lasting from a few seconds to several minutes.

Based on their duration, there are two kinds - Short GRBs that last 2 seconds or less and long GRBs that go on for more than 2 seconds.

Long GRBs originate from supernovas that mark the deaths of massive stars (>30 solar masses) and produce narrow beams of radiation as the star collapses.
Short GRBs are believed to result from the merger of compact stellar remnants such as neutron stars or black holes.

Initial explosion creates an ultra-relativistic jet of particles moving close to the speed of light, which in turn creates the burst of gamma rays as the particles interact with surrounding interstellar gas.

GRBs are detected approximately once per day from random directions in space by specialised satellites that monitor the cosmos for such intense bursts of gamma radiation.

GRBs can release more energy in 10 seconds than what our Sun will emit over its 10 billion year lifetime! Making them the most luminous and energetic events in the Universe.

Impact on Earth's Ionosphere:

Enhanced Ionisation: GRBs increase ionisation levels in the ionosphere, creating more ionised particles.
Radio Communication Disruption: This ionisation can affect long-range radio communications by changing the ionosphere's density, which alters radio wave paths.
GPS Inaccuracies: Changes in ionospheric density can also lead to GPS positioning errors.
Atmospheric Chemistry Changes: The burst can alter atmospheric chemistry, leading to new compound formations or destruction of existing ones.
Transient Luminous Events: GRBs may cause short-lived light phenomena in the upper atmosphere.
Satellite Damage Risk: Satellites in the ionosphere during a GRB face increased radiation exposure, potentially damaging their instrumentation.

Detection of Gamma-ray:

Fermi Gamma-ray Space Telescope: Equipped with two primary instruments - the Large Area Telescope (LAT) and the Gamma-ray Burst Monitor (GBM). LAT is used for observing gamma rays in the energy range from 20 MeV to over 300 GeV, while GBM detects lower-energy gamma rays.
Neil Gehrels Swift Observatory: This observatory carries three instruments: the Burst Alert Telescope (BAT), which detects gamma-ray bursts and computes their coordinates; the X-ray Telescope (XRT); and the Ultraviolet/Optical Telescope (UVOT). The XRT and UVOT are used for observing the afterglows of GRBs.
Hubble Space Telescope: While not a gamma-ray observatory, Hubble can observe the afterglows of GRBs in optical and ultraviolet light, providing valuable data on the distance and environment of the burst.
Chandra X-ray Observatory: This telescope, designed to detect X-rays from high-energy regions of the universe, can be used to observe the X-ray afterglows of GRBs.
Very Large Array (VLA): A radio astronomy observatory that can be used to observe the radio afterglows of gamma-ray bursts.
High Energy Transient Explorer (HETE): Previously used for detecting GRBs and providing rapid notification to ground-based observatories for follow-up observations.
Integral (International Gamma-Ray Astrophysics Laboratory): A European Space Agency satellite equipped with gamma-ray and X-ray monitors, useful in the study of GRBs.

Effect of Gamma-ray burst:

Intense Energy Release: GRBs emit vast amounts of gamma rays, the most energetic form of light.
Affecting Nearby Matter: This radiation can ionise gas, disrupt molecular clouds, and potentially trigger star formation nearby.
Altering Interstellar Medium: GRBs heat and ionise the space between stars and galaxies, impacting its evolution.
Cosmic Distance Measurement: GRBs help measure vast distances in the universe, aiding in cosmic mapping.
Risk to Planetary Life: A nearby GRB could harm a planet's atmosphere and life, but such events are extremely rare due to their distance and rarity.
Insights into Extreme Processes: They provide data on massive star deaths, black hole formation, and matter under extreme conditions.
Gravitational Wave Research: GRBs from neutron star mergers are important for studying gravitational waves.

What are Dark Matter and Dark Energy?

Context: The European Space Agency (ESA) has unveiled the first images captured by the Euclid space telescope designed to unlock the secrets of dark matter and dark energy. The primary objective of the telescope is to create the largest cosmic 3D map of the universe to better understand the distribution of dark matter and influence of dark energy in the early universe.

Dark Matter and Dark Energy:

Dark matter and dark energy together make up 95% of the universe. Around 68% of the Universe is made of dark energy while dark matter makes up 27%.
Only the remainder (5%) is composed of fermionic matter, i.e., things on the Earth, planets, stars, etc.

Dark Matter:

Dark matter is completely invisible and has not yet been observed directly. It does not interact with matter, emits no light or energy and thus cannot be detected directly by conventional sensors and detectors.
Scientists are confident it exists because of the gravitational effects it has on galaxies and galaxy clusters.

Dark Energy:

The existence of dark energy was theorised 25 years ago, when a team of researchers found that the expansion of the Universe was speeding up or accelerating, instead of slowing down due to gravity (inwards pulling force). Scientists have hypothesised that this is happening due to a mysterious form of energy called dark energy.

Characteristics of dark energy:

Dark energy has been hypothesised as a repulsive force or anti-gravity, i.e. while gravity tends to make objects attract, dark energy would pull them apart by increasing the space between them. Thus, dark energy has an expansionary effect. As our universe is expanding, it indicates that dark energy has a greater abundance than dark matter.
Dark energy is a property of space, so it does not get diluted as space expands.
- Normally, as the universe expands the density of mass and radiation in it decreases.
- However, the density of dark energy remains constant throughout. This means the dark energy in the universe is ever increasing, in order to keep the energy-density constant. Thus, dark energy should be energy inherent in the fabric of space itself.