Now that the JamesWebbSpaceTelescope has sent back its first images of deep space, you might be wondering what's coming next. Here's the scoop!
The world came together last week in a rare show of international unity to stare in wonder at the first scientific images produced by the James Webb Space Telescope. Decades in the making and the result of the efforts of thousands of people from around the globe, the telescope is set to revolutionize astronomy by allowing us to peer deeper into the cosmos than ever before.
Scientists knew these early galaxies were out there and were close to being accessible to us because the Hubble Space Telescope had observed some pretty early galaxies. When looking in the visible light wavelength, Hubble could identify hundreds of these galaxies, which formed within a few hundred million years of the Big Bang. But these galaxies had already formed, and researchers wanted to look back even further, to see them actually forming.
This is how Webb is able to detect and identify the very earliest galaxies. If Webb can see a galaxy that is shining brightly in the infrared, but which is dim or invisible to primarily visible light-based telescopes like Hubble, then researchers can be confident they’ve found a galaxy which is extremely redshifted – meaning it is very far away, and hence very old.
“The original focus of the telescope was much more on the high redshift universe,” McCaughrean summed up. “That was the highest goal, to find these first stars and galaxies that formed after the Big Bang. Everything else after that is a ‘nice to have.’ But over the progress of the project, we managed to turn that into four themes: cosmology, star formation, planetary science, and galaxy evolution. And we made sure that the observatory would be capable of all of those.
Cameras and spectrographs work together as well, as the filters used in imaging are useful for selecting objects to study with the spectrographs. Multiple modes To understand Webb’s full capabilities, you should know that the four instruments don’t have just one mode each – they can be used in multiple ways to look at different targets. In total, there are 17 modes between the four instruments, and each of these had to be tested and verified before the telescope was declared ready to start science operations.
This allows the light from the targets, such as particular galaxies, to shine through onto the telescope’s detectors, without allowing light from the background to leak through as well. “By only opening the door where the galaxy is and closing all the other doors, when the light comes through from that object, it gets spread out into a spectrum, and you don’t have all the other light coming through,” McCaughrean said. “That makes it more sensitive.
Both NIRCam and MIRI have coronagraphy modes, the simplest form of which is to place a small metal disk in front of the bright object to block out its light. Then you can observe the other, dimmer light sources around it more easily. But this approach has its limitations:if the bright object moves around behind the disk, its light can spill out over the edges and ruin the observations.
“So we can take a series of pictures over time with the same detector, as it builds up the light from the faint sources,” McCaughrean explains. “But when we look at the data, we can use the first images for the bright sources before they saturate, and then keep building up light from the faint sources and get the sensitivity. It effectively extends the dynamic range by reading the detectors out multiple times.
Challenges in working with Webb As with every piece of technology, there are limitations on what Webb can do. One of the big practical limitations for scientists using Webb is the amount of data that they can collect from the telescope. Unlike Hubble, which orbits around the Earth, Webb orbits the sun at a position called L2.
“People think space is cold, well, not if you’re next to a big object which is heating you up every day like the Earth or the sun,” McCaughrean said. “So if you want to look in the infrared, you need to make sure your telescope is incredibly cold, so it’s not emitting at the wavelengths that you’re trying to detect.” That’s why Webb has an enormous sunshield to help keep it cool, and why it is at L2 so the sunshield can block out heat from both the sun and the Earth.
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