Astronomers detect for first time light from very first stars of universe

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A team of astronomers including an Indian graduate student Nivedita Mahesh from Arizona State University have discovered for the first time signals from “cosmic dawn” – the moment when the universe’s earliest stars emerged, making a significant breakthrough in our understanding of the evolution of cosmos. The discovery, if confirmed, physicists say, could upturn our knowledge of the nature of still elusive ‘dark matter’


  • When the universe was formed in the Big Bang event 13.8 billion years ago there was no sun, no stars, no light, it was a dark place. 3,70,000 years after the Big Bang first atoms, primordial hydrogen was formed. Only when the universes cooled sufficiently for attractive force of gravity to overcome the repulsive thermal force the first stars emerged.
  • the first stars were born around 13.62 billion years ago in what astronomers call as ‘cosmic dawn’ when the whole universe was awash with ultraviolet rays, and first stellar death- explosions in supernovae, formation of stellar black holes, took place around 13.55 billion years ago. For comparison, Sun and Earth formed around 4.6 billion years ago.
  • Cosmologist came up with an ingenious idea to find when the early stars emerged. First stars rich in hydrogen were massive, tens and thousands time massive than our Sun. Massive stars live fast and burn out fast. The intense ultraviolet light from them would ionize the gas enveloping the stars. The ionized hydrogen gas would absorb the cosmic microwave background (CMB) radiation, the afterglow of the Big Bang at a characteristic wavelength.
  • “This intense ultraviolet light from the first stars could then interact with the hydrogen gas in the Universe, lowering its temperature below that of the ambient CMB radiation. This lets us see this hydrogen gas as a shadow against the brighter CMB in a particular frequency range. This causes dips in the brightness of CMB radiation in characteristic wavelength,”
  • As stars aged and ultimately died in violent explosions resulting in exotic neutron stars or black holes they emitted intense X rays which further ionised primordial hydrogen atoms. Highly ionised gas cloud would have fully muted the wavelengths. By looking for the dip in the brightness astronomers could infer when the first light dawned in the universe and by identifying when the characteristic wavelength was muted they can pinpoint when the first stars began to die.
  • In what is described as ‘searching needle-in-a-haystack’ operation, researchers intensely scanned the sky to detect even minuscule variation in the strength of the CMB radiation. The dips were seen to occur at wavelengths between 65 megahertz (MHz) and 95 MHz. Further booming signals emanating from natural sources in Milky Way galaxy were drowning out the measurement. The noise from other sources was about thousand to 10,000 times brighter than the signal. “It is like being in the middle of a hurricane and trying to hear the flap of a hummingbird’s wing,” as Peter Kurczynski, the NSF program director, put it.
  • The researchers used a table top-sized radio telescope called Experiment to Detect the Global Epoch of Reionization Signature (EDGES), based at the Murchison Radio-astronomy Observatory in the middle of Western Australian desert. Located far from cell phone towers, television and FM radio signals, this is one of the best ‘radio quiet’ places in the world. EDGES could capture faint signals from the outer reaches of the universe. After the strenuous search, researchers found, the dip, just 0.1% drop in the radiation at roughly the frequency they expected.
  • Before the first stars, the universe had just hydrogen and some helium atoms. Heavier elements like carbon, oxygen and so on were cooked inside the stellar crucible subsequent to comic dawn. Life as we know is carbon-based and understanding the ‘cosmic dawn’ is crucial to understand our cosmic evolutionary ladder.
  • The study not only establishes the time scale of Cosmic Dawn phase of the evolution of the cosmos but also gives us clues as to the mysterious dark matter, about which we are literally groping in the dark,”
  • Meanwhile, astronomers around the world are proposing to train the Hydrogen Epoch of Reionization Array, an international radio-telescope project based in South Africa’s Karoo desert, and the LOFAR (Low-Frequency Array), a large system of radio antennas spread over five European countries to get an independent verification. “The Giant Metrewave Radio Telescope near Pune operated by the National Centre for Radio Astrophysics (NCRA-TIFR) is well suited to detect these variations,” says says Prof. Tirthankar Roy Choudhury of NCRA-TIFR.

Q.1 Consider the following statements with respect to Dark matter

  1. Dark matter only interacts by way of gravity and the weak atomic force.
  2. Dark matter does not interact via either the strong atomic force or electromagnetism.

Choose the correct answer from the above

  1. 1 only
  2. 2 only
  3. Both 1 and 2
  4. Neither 1 nor 2

Answer: c.) both 1 and 2

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