The James Webb telescope explodes on a mission to observe the infant universe

The most ambitious and expensive telescope ever built was launched into space on Christmas Day, with the aim of looking deeper into space – and thus back in time farther than ever before.

After three decades of planning and construction beset by delays and escalating costs, the $10 billion James Webb Space Telescope is finally on its way to an extraordinary orbit, four times farther from the Earth than the Moon.

At the European Space Agency’s control center in Kourou, French Guiana, scientists and engineers cheered and clapped at the crucial moment marking a successful launch, when the telescope separated. from the upper stage of the Ariane 5 rocket after 27 minutes and began an independent journey to its observation point 1.5m km away.

“This is a great day not only for the US and our European and Canadian partners, but also for the world,” said Bill Nelson, head of the US space agency who led the international project. A great day for planet Earth.

Webb’s primary purpose was to image the first stars and galaxies that formed from primordial gas during the “cosmic dawn” some 200m years after the Big Bang.

But astronomers also expect the Webb telescope to provide a treasure trove of observations of objects closer to home, especially planets — both within our own solar system and the stars orbiting distant stars. elsewhere in the galaxy. Its instruments will measure the chemical composition of the planet’s atmospheres, looking for the molecular building blocks of life.

Richard Ellis, professor of astrophysics at University College London, has been involved in the project since the early 1990s, when the US space agency Nasa assembled a science team to plan a successor to the observatory. recently launched Hubble probe. It was named James Webb after the director of Nasa, who led the Apollo program in the 1960s.

“It became very expensive, there were a lot of postponements and Webb was threatened with cancellation many times,” Ellis said. “But now, at last, we have a telescope that astronomers are very excited about and proud of.”

An informative image explaining the components of the James Webb . Space Telescope

Webb’s 6.5 meter primary mirror makes it 100 times more powerful than Hubble. But the main difference between the two large telescopes is that Hubble observes visible light, while Webb operates in the infrared. The latter is much better for detecting very distant objects because their light is converted to longer wavelengths by the expansion of the universe.

While Hubble in low orbit is only 550 km from Earth, Webb will be 1.5m km away at the “second Lagrange point”, or L2. Here, gravity from the Sun and Earth exactly balances a satellite’s orbital motion, so it appears to hover at the same place in space.

L2’s advantage over low Earth orbit is that its great distance from the planet makes it much easier to keep Webb cool and protected from Earth’s infrared radiation. One disadvantage is that it is too far away to reach a maintenance and repair mission should something go wrong. The famous Hubble was saved from a nightmare in 1993, when the Space Shuttle astronauts installed corrective optics on its faulty mirror.

Diagram explaining why the James Webb Space Telescope will observe objects in infrared wavelengths and redshifts

Webb will take about a month to reach L2. Along the way, it will open up the main mirror, made of 18 gold-coated beryllium metal hexagonal plates and a giant sunshade, about the size of a tennis court and will keep the telescope in the dark. permanently at an expected temperature of -233C.

But even that wouldn’t be cold enough for one of Webb’s four devices, medium infrared, or MIRI. It will be brought down to -266C, just seven degrees above absolute zero, with a chiller. Gillian Wright, Director of the UK Center for Astrotechnology in Edinburgh and co-leader of the MIRI team said: “It works on the same principle as your fridge in your home, except that the coolant is helium, in liquid at extremely low temperatures.

MIRI will play a key role in detecting the first stellar flash through thick clouds of proto-gas during cosmic dawn and in analyzing the atmospheres of distant planets. But when asked which observation she was most looking forward to, Wright replied: “I’m most excited when I find something completely unexpected. We’ve never had a mid-range infrared device like MIRI in space before and it’ll find things we don’t know about it now. “

Wright added that Webb and its tools will go live with a series of operational observations during April and May to check that everything is working properly. Astronomical research will then begin around July.

Diagram explaining the position of the James Webb Space Telescope in orbit

The Space Telescope Science Institute in Baltimore has allocated observation time to astronomers on Hubble for 30 years, and will do the same for Webb. The slots are oversubscribed so a peer-review system is used to decide who should get them, with some reserved for scientists involved in making instruments for telescopes.

Wright said her team will be intensively examining a small region of the sky that Hubble has studied known as the Hubble Deep Field to look for super faint and extremely early galaxies. “We also have a big program looking at planetary atmospheres,” she said. Another question scientists want to answer is how exoplanets – orbiting stars elsewhere in our galaxy – form from cosmic dust.

Although the Christmas Day launch went perfectly, astronomers now have to endure what Ellis calls “several months of suffering,” waiting for Webb to complete an extensive series of exercises and operate the instrument. be complicated.

If the telescope works well, it holds great scientific promise – an astronomical Christmas present that could last for a decade.

“I have been studying the early evolution of galaxies for many years,” says Ellis. “Getting a glimpse of the ‘cosmic dawn’ with Webb would be the pinnacle of my career.”

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