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The sky is large. If you want to map it in detail, you have to think big too.
Astronomers are good at it. A huge international team has just published a study of the sky so huge that I find it hard to grasp it.
The map is the culmination of six years with 1,405 nights of sightings, three telescopes (and a space telescope), and a data-cranking supercomputer … because the survey has a total of 10 thousand billion pixels, and is a petabyte of data – one thousand terabytes or one million gigabytes.
Oh it’s also over a billion galaxies in. One billion.
As I said: Vast.
This is the result of DESI Legacy Imaging Surveys, sky maps carried out by the three observatories (the Dark Energy Camera Legacy Survey, the Beijing-Arizona Sky Survey and the Mayall zband Legacy Survey, in combination with the WISE infrared observatory in orbit). They mapped the northern sky in seven colors, covering a third of the entire sky – 14,000 square degrees, or the equivalent area of 70,000 full moons on the sky.
The ultimate goal is to better understand dark energy, the mysterious substance that accelerates the expansion of the Universe, by looking at the distribution of galaxies throughout the Universe. They will do this by selecting tens of millions of the billion galaxies in the data and obtaining follow-up observations with the Dark Energy Spectroscopic Instrument (DESI), which will take the spectra of these galaxies and find their distances.
Since we will know their positions in the sky and their distances, this will make a 3D map of the Universe bigger than ever.
Also like I said: Think large.
Spectroscopic observations won’t be made until 2024, but there has already been an abundance of science from the survey observations.
For example, astronomers – including ‘citizen scientists’, just people passionate about science who don’t necessarily have a formal scientific background – have selected the data for brown dwarfs, objects of mass intermediate between planets and stars, and found 525 of them about 65 light years from the Sun in records, 38 of which had never been seen before. Combined with data from the Spitzer Space Telescope, they were able to obtain the distances, making this the best 3D map of brown dwarfs to date.
Because the survey includes infrared light, it is sensitive to hot objects like brown dwarfs, and they believe this survey should see any brown dwarf within 65 light years that are warmer than around 330 ° Celsius ( 620 ° F). They’re getting colder than that – in fact, brown dwarfs were found a few years ago that are actually at room temperature, and there may be even cooler ones out there – so it’s possible there are still have many others to detect. Still, it’s a great start! Brown dwarfs are weak (the first was not even discovered until the 1990s) and hard to find.
This sort of thing is important because we know that stars form when clouds of gas and dust collapse, but when it does, stars of all different masses are born. Massive stars are bright so easy to see, but at the low mass end the stars are pale. However, many more of them are created than high mass stars, so to get a census of objects we need to better understand this lower end of the spectrum. This survey will help you.
Another group of astronomers looked at objects much further away – individual galaxies as well as clusters of galaxies – in order to find gravitational lenses. When light from an even more distant galaxy passes by a galaxy or cluster on its way to Earth, the intervening object’s gravity bends that light’s path like a lens, creating distorted images of the background galaxy. The light can also be amplified a bit, which makes paler objects brighter.
This phenomenon makes it possible to observe weak and distant galaxies and to see what is happening there. It also tells us about the distribution of mass and dark matter in clusters of galaxies and galaxies, so it’s a double.
The group applied machine learning to DESI data, teaching an algorithm how to find gravitational lenses in observations… and hoo my, it’s done. He found over 1,200 new objectives, doubling the number known so far! I will note that they are technically candidate lenses, which need to be confirmed, but they inspected them visually so I’m confident the majority of them are real.
It’s really just a taste of what’s possible. Huge surveys like this are treasure troves, just huge stacks of data waiting for scientists to dive in and use it for all the research they do. It is their beauty. They’re generalized, so if you’re studying brown dwarfs or gravitational lenses, bright stars or dwarf galaxies or galaxy collisions, whatever, there will likely be something useful in the investigation.
You can also view the interactive viewer created by the team yourself. It’s pretty intuitive; you can scroll in and out, move around or search for your favorite object … as long as the survey covers that part of the sky. There is also a chat room where (if you sign up) you can report interesting items and discuss them with others. You might discover something!
Enjoy. With over a billion objects in the database, this should keep everyone busy for a long, long time.
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