The Universe is over 13 billion years old, so a 12-year slice of that time may seem uneventful. But a NASA sped-up movie shows just how much that can change in just over a decade. Stars pulsate, asteroids follow their trajectories, and distant black holes flare up, pulling gas and dust towards them.
NASA launched WISE – the Widefield Infrared Survey Explorer – in 2009. WISE has found star clusters, thousands of dwarf planets, and helped discover Earth’s Trojan asteroids, among other things. When WISE ran out of primary coolant in 2011, NASA put the spacecraft into hibernation. But some of the spacecraft’s infrared detectors were still working. So, in 2013, they reactivated the mission as NEOWISE—Near-Earth Object Wide Field Infrared Survey Explorer. One of the main objectives of NEOWISE was to characterize 2,000 known asteroids.
The spacecraft did these things by taking wide-field surveys of the sky. Every six months, NEOWISE completes an image of the night sky. NASA combined 18 of these images of the entire sky taken over a decade to create a timelapse of the night sky. Together they contain hundreds of millions of objects.
![Universe today](https://oponame.com/wp-content/uploads/2022/10/Shortly-before-they-collided-two-black-holes-tangled-spacetime-into.png)
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“If you go out and look at the night sky, it might seem like nothing ever changes, but it doesn’t,” said Amy Mainzer, principal investigator for NEOWISE at the University of Arizona in Tucson. “The stars shine and explode. The asteroids pass at full speed. Black holes tear apart stars. The Universe is a very busy and active place.
One of the mission’s important contributions to science is its study of brown dwarfs. Brown dwarfs aren’t quite stars; they are substellar objects on the way to becoming stars. But they never mustered enough mass to trigger hydrogen fusion. They are smaller than stars and larger than the largest planets. Their masses range from about 13 to 80 Jupiter masses.
![Brown dwarfs are too big to be planets, but not massive enough to be stars. Credit: NASA/JPL-Caltech](https://oponame.com/wp-content/uploads/2022/10/NASA-provides-time-lapse-movie-showing-how-the-universe-has-changed.jpg)
Astrophysicists theorized that brown dwarfs existed, but only infrared observations could find them. Infrared astronomy is difficult from the Earth’s surface, although the 2MASS survey managed to find some. We now know thousands of them, thanks to infrared observatories like WISE/NEOWISE.
Astrophysicists are interested in the coolest brown dwarfs because they bridge the gap between stars and planets. They are spectral class Y brown dwarfs and emit very little energy. The cooler ones are a little more than room temperature. WISE discovered class Y brown dwarfs in 2011.
NASA eventually combined data from WISE and NEOWISE into a catalog called CATWISE. In 2019, scientists browsing the catalog found CWISEP J1935-1546, an even cooler brown dwarf with an estimated temperature of 270–360 K (?3–87 °C; 26–188 °F).
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Citizen scientists have also played a role in NEO/NEOWISE’s brown dwarf activities. Citizen scientists have helped find two of the most unusual brown dwarfs ever discovered. They’re called T-type subdwarves, and scientists and volunteers found them in 2020 as part of the Backyard Worlds project.
In 2020, scientists working with NEOWISE discovered the strangest brown dwarf to date. They nicknamed it “The Accident” because they found it by chance. The Accident is old – between 10 and 13 billion years old – and has a very low metallicity. It is so old that its metallicity reflects the early Universe rather than the modern Universe. Generations of stars have created heavier elements and dispersed them into space over billions of years, so objects formed in more recent times have higher metallicities.
![This artist's illustration shows a cold, dark brown dwarf in space. Brown dwarfs form like stars but don't have enough mass to trigger nuclear fusion in their cores - the process that causes stars to burn up. As a result, they share certain physical characteristics with massive planets like Jupiter. Image credit: IPAC/Caltech](https://oponame.com/wp-content/uploads/2022/10/1666668024_760_NASA-provides-time-lapse-movie-showing-how-the-universe-has-changed.jpg)
Although the Crash is the first of these ancient brown dwarfs ever found, it probably won’t be the last. There are probably many lurking in the dark, perhaps even still hidden in the NEOWISE data.
The NEOWISE mission lasted much longer than expected. When NASA launched it as WISE, they thought it would last about two years until its coolant ran out. But after having put it back into service under the name of NEOWISE, the mission has lasted for ten years. Even the WISE scientists are surprised at the length of the mission and the amount of data collected.
“We never expected the spacecraft to run for this long, and I don’t think we could have anticipated the science that we would be able to do with this much data,” said Peter Eisenhardt, an astronomer at the Jet Propulsion Laboratory in NASA and WISE Project Scientist.
If you want to help scientists use all the data from NEOWISE and maybe even find one of the elusive ancient brown dwarfs like The Accident, check out Backyard Worlds: Planet Nine.
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