James Webb: Before the launch of the space telescope, four reasons to say “thank you” to your little brother… – 20minutes.fr

James webb here, James Webb there. He has not yet left the cow’s land, and he is still far from having come to the end of the path strewn with pitfalls to
Lagrange point L2 (1.5 million kilometers from Earth) , where it will be put into orbit. However, the future space telescope, whose launch is
scheduled for December 22 [pas avant le 24 décembre,
dit désormais Arianespace], already spills a lot of ink.

I have to say that expectations are high for the largest and most powerful telescope ever launched into space. No doubt Hubble will then live in the shadow of its little (but much bigger) brother. But be careful not to disrespect him. In orbit 590 kilometers from Earth since 1990, the first space telescope has made more than a million observations, with important findings. 20 Minuteits selected four reasons to say a huge “thank you”.

For your beautiful images

In thirty-one years, it’s not a little to say that Hubble has wowed us. One of his most famous images is the one taken on April 1, 1995. “Pillars of Creation”, these gigantic columns of gas and dust of the Eagle nebula which act as a nursery of stars. But there are many, many others, some just as breathtaking. A quick glance at the
Hubble twitter account, where NASA publishes pictures of the telescope daily, is enough to realize this.

This is the big “plus” of a space telescope compared to ground observatories. “These are limited by the atmosphere, which blocks certain wavelengths including ultraviolet (and luckily for us!) But also scrambles the images *”, begins Thierry Contini, astrophysicist atInstitute for Research in Astrophysics and Planetology (IRAP). Nevertheless, “even with a relatively modest mirror (2.40m in diameter), Hubble was able to take finer, more precise images than the giants of the ground”, continues Oliver Sanguy, editor-in-chief of space news. at
Toulouse Space City.

And grandiose as a bonus. An asset that NASA has been able to fully exploit to provide scientific mediation and interest the general public in astronomy. “It was, from the start, one of the missions set for this Hubble program,” recalls Olivier Sanguy.

For being so prolific

Hubble hasn’t just wowed the gallery for the past three decades. It is also and above all one of the most productive scientific instruments ever designed. At the last count, this summer, NASA estimated at 1.5 million the number of observations made by Hubble, which gave rise to 18,000 scientific articles, in turn cited more than 900,000 times. “A total which increases, on average, by more than 150 per day”, specifies the American space agency.

Again, being in Space helps a lot. “Hubble does not know the weather problems nor the day / night alternation, illustrates Olivier Sanguy. And if certain portions of the sky are inaccessible to him – those too close to the sun, for example -, he still has an important observation window in which he was able to respond “. Even at 590 km from us, “Hubble can be piloted like any ground observatory, with the possibility of aiming it, at any time and quickly, on a specific region of the sky,” explains Thierry Contini. For example, he made some very beautiful images of the collision of comet Shoemaker-Levy with Jupiter in 1994. In the fall of 2017, Hubble was also one of the telescopes used
to learn more about the origin of the gravitational wave source [des oscillations dans la courbure de l’espace-temps produites par les phénomènes les plus violents du cosmos] detected a few months earlier by
interferometers Ligo, in the United States, and Virgo, in Italy. “

For teaching us to better understand the Universe

The planets of the solar system, nearby galaxies, exoplanets, stars, their nurseries. In thirty-one years, the telescope has fixed its eye on multiple celestial objects. With, at the end, “major discoveries for generations of astrophysicists, assures Thierry Contini. It is to him, for example, that we owe the confirmation of the existence supermassive black holes in the heart of large galaxies. “

We also owe a lot to Hubble in the distant Universe. “Originally, its main mission was to know more precisely the age of the Universe,” explains Olivier Sanguy. Before its launch, it was estimated to be between 10 and 20 billion years old, a very wide range. The observations of sepheids and supernovae that Hubble was able to make ** allowed us to arrive at an estimate of 13.7 billion years (+/- 10%). “

So much for the age. Hubble has also helped improve our understanding of the structure of the Universe. Another famous image of the telescope is that of the “Hubble deep field”, a tiny patch of sky in the constellation Ursa Major that Hubble observed over ten consecutive days, from December 18 to 28, 1995. While the result is visually less breathtaking than the Pillars of Creation, the “deep field of ‘Hubble’ is one of the most distant images of Space we have. And just in this tiny corner of the sky, Hubble has found several thousand galaxies. Much more than expected, which prompted to revise upwards the estimate of the number of galaxies in the Universe. “From 200 billion in the observable Universe to 2,000 billion today,” says Oliver Sanguy.

Hubble has made it possible to go further and in unexpected ways. The farthest supernovae he observed appeared less bright than expected, “meaning that theexpansion of the Universe is accelerating instead of slowing down ”, explain the astronomers Thibault Merle and Alain Jorissen in
The Conversation. A fragile hypothesis at the beginning but which has not ceased to be confirmed since.

To continue the job for several more years

“One of the most important fields of progress in astronomy is in the infrared”, launches Olivier Sanguy. Electromagnetic radiation of the same nature as visible light, but whose wavelengths are too long to be perceptible by the human eye.

James Webb will be optimized to observe in the infrared, the near and the medium, with this beautiful promise then to be able to observe very distant objects and, thus, to go back even further to the origins of the Universe. “But it will only do that when Hubble covers everything else, that is to say visible light, ultraviolet, but also near infrared”, continues Olivier Sanguy. “Frequencies that continue to interest us in astrophysics”, specifies Thierry Contini.

It would be a shame then to do without Hubble, especially since it was designed and placed in orbit at a distance close enough to Earth to be able to be repaired and updated. Clearly, Hubble is far from being rusty. “Its lifespan is impressive, and while it seemed agreed that he would retire with the arrival of James Webb, NASA decided to keep him in service for at least ten years”, says the astrophysicist of IRAP. Who sees it as a very good decision: “there are great complementarities to be found between the two telescopes, including in the observation of common celestial objects,” he begins. And it will most likely be difficult to get “telescope time” with James Webb, which is expected to be in high demand, so Hubble will still be doing a lot of service. “