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A powerful new “eye” in the sky



Today we are on the threshold of a great “astronomical revolution”, a revolution that will show the universe in a whole new light. At 6:20 pm Bangladesh Standard Time, NASA is expected to launch the James Webb Space Telescope, the next-generation telescope that “will serve as deep space’s premier observatory for the next decade” into orbit. The $ 10 billion, 6200 kg telescope, simply called Webb, will take off from a launch site in French Guiana for its celestial home, L2 Lagrange Point, about 1.5 million kilometers from Earth.

What is L2? It is a point in space – there are four more – determined by the 18th century Franco-Italian mathematician Joseph-Louis Lagrange at which a satellite, under the gravitational influence of the Earth and the Sun, will remain approximately at the rest from them. The tip can therefore be used by Webb as a “parking space” to maintain a stable position, with minimal fuel consumption during its turn around the Sun.

At L2, which is directly behind Earth as seen from the Sun, Webb will always be in the same location relative to Earth. As a result, astronomers can have continuous communications with Webb while the Earth rotates. Additionally, Webb will always see the Sun, Moon, and Earth on one side, with an unobstructed view of deep space on the other side, making him ideal for seeing much further into the universe.

It will take about a month for Webb to reach his destination and deploy his mirrors and a tennis court-sized sunshade. The shield will protect the telescope by blocking light and heat from the Sun, Earth, and Moon. Scientists will need another five months to align the mirrors and cool the instruments to their operating temperatures. Approximately six months after launch, Webb will begin collecting and reporting data.

Among the pantheon of space telescopes, the Hubble Telescope, placed in orbit by the Space Shuttle Discovery in 1990, is the most famous observatory in space. At an altitude of about 560 km, Hubble orbits the Earth every 97 minutes, or 15 orbits per day, with an orbital speed of 28,000 km per hour. Far above the rain clouds, free from light pollution, and free from the distorting effects of the Earth’s atmosphere, Hubble can operate around the clock with a breathtaking view of the universe.

The Hubble domain stretches from ultraviolet to visible and near infrared. This range has enabled Hubble to deliver stunning images of stars, galaxies and other astronomical objects that have changed our understanding of the universe beyond measure. However, as big as Hubble is, it may have reached its limits, although its importance shouldn’t fade anytime soon.

Why do we need Webb?

Electromagnetic radiation, ranging from gamma rays to radio waves, is our measuring stick in space. It is the cosmic messenger who carries much more information than any other messenger. That said, many of the objects we want to observe in space are too cold to emit visible light or other forms of short wavelength radiation. Instead, they emit long wavelength infrared light. The reason is that the wavelength of light leaving the stars and galaxies of the early universe, initially shortwave and highly energetic, has been shifted towards the infrared by the Doppler effect. This is a stretch of the short wavelength of light to larger values, as the light sources move away from the observer during travel to Earth due to the continued expansion of the universe. In astronomical jargon, this is called “the cosmological redshift”.

In many ways, Hubble’s infrared views are fundamentally limited by its very design. Specifically, the telescope’s perch in low Earth orbit – where it has to face not only radiation from the Sun, but infrared light radiated and reflected from the Earth itself – interferes with any attempt to observe infrared light. of the cosmos. Hence the Webb, designed to take us far beyond the Hubble limit. In particular, Webb will be observing primarily in the infrared region, which will show us things never seen before by Hubble or any other telescope.

With a 6.5 meter diameter primary mirror shaped like a “golden sunflower” and a cryogenic operating temperature — about 225 degrees Celsius below zero — Webb will be the largest and most powerful space telescope — 100 times more powerful. than Hubble — never built with unprecedented sensitivity. The dimension of Webb’s mirror will result in a 6.5-fold increase in the size of the data collection area, as opposed to other telescopes.

But why does Webb have to be cooled to extremely low temperatures? As noted above, Webb is designed to detect weak infrared signals from objects located billions of light years away (1 light year = 9.46 trillion kilometers). In order to detect these signals, which can sometimes be felt as heat, the instruments inside Webb must be kept at very cold temperatures. Otherwise, all Webb will detect is its own infrared radiation.

Webb’s mission

Webb’s main mission is to unravel the lingering mysteries of the universe. To this end, astronomers and cosmologists hope to use the telescope to travel back in time 13.5 billion years, which is closer to the beginning of time, and see some of the first galaxies to form in the universe. . Hubble cannot see these galaxies because of the redshift. Additionally, Webb will be able to look inside the dust clouds where stars are forming today. In addition, Webb will provide information on the formation of planetary systems, including our own solar system, looking for vital exoplanets inside our galaxy (the Milky Way) and looking for signs of extraterrestrial life.

Webb’s exceptional infrared imaging power will give researchers new views of three active supermassive black holes called quasars, their host galaxies and their neighborhoods, located more than 13 billion light years away. In addition, Webb will allow astronomers to observe gravitational distortions, a consequence of Einstein’s general theory of relativity, caused by smaller black holes with a mass only 100,000 times the mass of the Sun. Webb will also discuss how galaxies obtained supermassive black holes at their centers. In addition, astronomers hope to use Webb to find the origin of the violent eruptions of light from the colossal black hole Sagittarius A *, located in the center of our galaxy.

Cosmic Dark Ages and the Webb

One of the unsolved problems in cosmology is the structure of the universe from the first few minutes to about 300,000 years after its creation 13.7 billion years ago. This period was filled with obscurity, both literal and metaphorical. This is why astronomers call this period the cosmic dark age. We know very little about this time period as light could not escape from its surroundings across the universe to hit the detectors here on Earth. The emergence of the first sources of light, which are stars and galaxies formed by gravity, marked the end of the Dark Ages.

Webb’s design offers a unique ability to answer key questions about this era of cosmic evolution. Most importantly, Webb should provide answers to the following questions: When and how did the Dark Ages end? What is the nature of the first galaxies? How and when did the ionization of space between galaxies occur? And what sources caused the ionization? (Ionization is the process by which an electrically neutral atom charges negatively or positively by gaining or losing electrons.)

Webb’s lifespan will be dictated by how much fuel it uses. Unlike Hubble, which has been in operation for almost 32 years, Webb is expected to operate for at least five years – perhaps, with any luck, up to 10. It is not designed to be refueled, repaired or upgraded. level in any way. just because it will be so far from Earth. When Webb runs out of fuel, it will no longer be able to maintain its orbit and therefore will not be able to point its targets of interest with the required precision. And that will be the end of Webb’s mission.

Nonetheless, during his short life, Webb will explore every phase of cosmic history that will help us understand the origin of the universe. He will rewrite the history of the cosmos and reshape the position of humanity within it by piercing the “black curtain” until then of the primitive universe.

Dr Quamrul Haider is Professor of Physics at Fordham University in New York, USA.