The sky is big. If you want to map it in detail, you also have to think big.
Astronomers are good at that. A huge international team has just released an aerial survey so big it’s hard for me to comprehend.
The map is the culmination of six years with 1,405 nights of observations, three telescopes (and one space telescope), and one supercomputer cranking the data away … as the survey took a total of 10 trillion pixels, and forms a petabyte of data – a thousand terabytes or a million gigabytes.
Oh, it’s over too a billion galaxies in the. A billion.
Like I said: huge.
It is the result of the DESI Legacy Imaging Surveys, maps of the sky created 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 orbiting WISE infrared observatory). They mapped the northern sky in seven colors, covering one third of the entire sky – 14,000 square degrees, or the equivalent area of 70,000 full moons in 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 that by selecting tens of millions of the billion galaxies in the data and making follow-up observations with the Dark Energy Spectroscopic Instrument (DESI), which will take spectra of those galaxies and determine their distances.
Knowing their position in the sky and their distances will make a 3D map of the Universe bigger than ever before.
Also like I said: think big.
The spectroscopic observations won’t be made until 2024, but there is already a neat wealth of science from the survey observations.
For example, astronomers – including “ citizen scientists, ” just science-loving people who don’t necessarily have a formal science education – searched for brown dwarfs, objects of average mass between planets and stars, and found 525 of them within about 65 light-years of the sun in the Sun. studies, of which 38 had never been seen before. Combined with data from the Spitzer space telescope, they were able to determine the distances, making this the best 3D map of brown dwarfs to date.
Because the study includes infrared light, it is sensitive to warm objects such as brown dwarfs, and they think this study should see any brown dwarf closer than 65 light years warmer than about 330 ° Celsius (620 ° F). They’re getting cooler than that – in fact, some brown dwarfs were found a few years ago that are actually at room temperature, and there may be even cooler ones – so it is possible that there are many more to be discovered. Still, this is a great start! Brown dwarfs are weak (the first was not discovered until the 1990s) and difficult to find.
This kind of thing is important because we know that stars form when clouds of gas and dust collapse, but when they do, stars of all different masses are born. Massive stars are bright so they are easy to see, but their low mass makes the stars faint. However, much more are made of them than high-mass stars, so to get a count of objects we need to better understand that weak end of the spectrum. This survey will help.
Another group of astronomers looked at objects much more distant: individual galaxies and galaxy clusters, to find them gravity lenses. When light from an even more distant galaxy passes near a galaxy or cluster on its way to Earth, the gravity of the intermediate object bends the path of that light like a lens, creating distorted images of the background galaxy. The light can also be boosted considerably, making fainter objects appear brighter.
This phenomenon makes it possible to observe faint, distant galaxies and see what is happening inside them. It also tells us about the distribution of mass and dark matter in the Milky Way and galaxy clusters, so it’s a twofold one.
The group applied machine learning to the DESI data and taught an algorithm how to find gravitational lenses in the observations … and ho, did it. More than 1,200 new lenses have been found, doubling the number known so far! I note that they are technical candidate lenses, which need to be attached, but they visually inspected them so I’m sure most of them are real.
This is really just a taste of what is possible. Massive studies like this one are treasure troves, just huge piles of data waiting for scientists to dive in and use it for whatever research they do. That’s the great thing about them. They’re generalized, so if you’re studying brown dwarfs or gravitational lenses or bright stars or dwarf galaxies or galaxy collisions, whatever, there is probably something useful in the study.
You can also take a look yourself in the interactive viewer that the team has created. It’s fairly intuitive; you can scroll in and out, walk around or search for your favorite object … provided that the survey covered that part of the sky. There is also a chat room where you (if you register) can point out interesting objects and discuss them with others. Maybe you will discover something!
Lots of fun. With over a billion objects in the database, this should keep everyone busy for a long time.