25 of the Greatest Hubble Telescope Discoveries From the Past 25 Years  

Astronomers are rightly celebrating all the amazing scientific discoveries made by the Hubble Space Telescope on the device’s 25th birthday. But it had a rough start: Right after Hubble launched, it was unclear whether telescope would provide anything useful at all; the first pictures turned out blurry, thanks to an improperly ground mirror. However, astronauts were able to go up and install an arrangement of mirrors that acted as eyeglasses for Hubble’s blurry vision. Ever since then, Hubble’s been sending back some of the most beautiful images of the universe ever seen—and contributed enough data for more than 9,400 scientific papers. In honor of Hubble’s silver anniversary, here are 25 of our favorite findings from the telescope’s 25-year mission.

1. Just how old is the universe?

Before Hubble began taking shots of the cosmos, estimates for the age of the universe ran between 10 and 20 billion years old. But Hubble was able to help nail down a more precise age of around 13.7 billion years by taking pictures that helped scientists calculate the current expansion rate of the universe. One key element was Hubble’s observations of special types of bodies called Cepheid variable stars, which have very stable patterns of brightness that make them very effective at measuring distance. The Cepheids proved to be reliable signposts for the pace at which galaxies are moving away, which in turn gave us a more precise birthday for the universe. Hubble also uses other methods to cross-check this estimate, including looking for extremely old white dwarf stars.

2. Seeing starbursts

An unexpected event in space occurred in 2002, when a star in the constellation Monoceros suddenly became very bright. Hubble swung its gear around to see what was up. It caught a series of stunning images of light-illuminated shells of dust surrounding the star V838 further and further outward—a never-before-seen effect called a light echo.

Credit: ESA, NASA, Hubble Space Telescope

3. Gazing into stellar nurseries

The key to making a star is dust, lots of it. Before Hubble was operational, astronomers could never see the vast disks of material in stellar nurseries, only the bright jets of radiation thrown off by the forming star. With Hubble, we can get a glimpse of both the dusty star-forming material and the glowing jets. And these stellar nurseries often make for the most breathtaking pictures.

4. Keeping an eye on the neighborhood

Hubble can also draw its focus on objects closer to home. The space telescope has discovered new features on Neptune, and spotted the fallout from comets striking Jupiter, among many other insights into our solar system.

5. First visible light image of an alien world

The star Fomalhaut (seen in the Southern Fish constellation) was long thought to harbor planets before Hubble first focused on it in the early 2000s. Soon they found that the ring of icy and rocky debris surrounding the star had a sharp inner edge likely formed by the gravitational influence of a planet. By 2008, researchers had succeeded in getting a picture of that planet, Fomalhaut b, which seems to be at most three times as massive as Jupiter.

6. Calculating the age of the “Methuselah Star”

The “Methuselah star,” a fast-moving visitor to our region of the Milky Way, has been known to astronomers for a century. While it was known to be an old star, its actual age had long escaped discovery. In 2000, astronomers arrived at an estimate of 16 billion years, which would be impossible, given that the universe is just 13.8 billion years old. By 2013, Hubble observations allowed cosmologists to scale that figure back to a more reasonable 14.5 billion years, plus or minus 800 million years—thus putting it within the realm of compatibility.

7. Untangling a dark matter mystery

Hubble is frequently marshaled to help out in collaborative projects. Recently, Hubble’s visible light observations of 72 colliding galaxy clusters were combined with X-ray images of the collisions taken by the Chandra X-ray observatory. The composite image gives researchers a window into the mysterious web of dark matter that lurks in the clusters wherever it shows signs of gravitational lensing. By looking at how light from beyond the collision is distorted by the gravitational effects of dark matter, researchers can map the distribution of that invisible substance.

8. Clocking the universe’s expansion

For some time it was thought that the expansion of the universe set in motion by the Big Bang must be slowing down after that initial push. But Hubble observations of supernovae helped show that, counterintuitively, the expansion of the universe is actually speeding up. This discovery clued scientists in to the existence of a mysterious agent called “dark energy” that is somehow accelerating the outrushing expansion.

9. Spotting dark energy in the early universe

Was the dark energy that’s repelling the universe away from itself created in recent history, or has it been with us the whole time? Hubble’s pictures of supernovae helped researchers determine that dark energy has been with us for a very long time, accelerating the expansion of the universe as long as nine billion years ago.

10. Seeing deep

The first Hubble Deep Field image was made in 1995, over a 10-day period of observation. Researchers combined 342 separate exposures of the selected area of sky in Ursa Major, which looks empty to our vantage point from Earth. But once the pictures resolved, scientists were able to pick out nearly 3,000 separate galaxies, dating back to the earliest days of the universe. Another Deep Field image, covering a different section of sky, was created in 1996, followed by the Hubble Ultra Deep Field in 2004 and the Hubble eXtreme Deep Field in 2012. This latest image includes 22 days of exposure time and allows astronomers to peer at stars forming 5 to 10 billion light years away.

Credit: NASA, ESA, H. Teplitz and M. Rafelski (IPAC/Caltech), A. Koekemoer (STScI), R. Windhorst (Arizona State University), and Z. Levay and G. Bacon (STScI)

11. Searching for a new horizon for New Horizons

For a long time, it wasn’t clear what the New Horizons spacecraft was going to do once it finished touring Pluto. But Hubble assisted in locating some interesting targets for the spacecraft out in the Kuiper belt, a region of icy bodies orbiting out past Neptune. The most likely target, dubbed PT1, might prove to be a valuable time capsule from the earliest days of our solar system.

12. Spotting a six-tailed asteroid

In 2013, Hubble found a very unusual asteroid sporting six tails of dust. The tails, NASA scientists think, are caused by the rotation of the asteroid itself, not by an impact with another body. This kind of rotational breakup may actually be a common cause of death for asteroids across the solar system.

13. Finding water on other worlds

In the search for extraterrestrial life, the presence of water is one of the most important ingredients we’re looking for on exoplanets. So when Hubble picked up a “clear signal” of water in the atmospheres of five alien worlds, scientists were heartened—not so much by the planets themselves; they’re all “hot Jupiter” type planets. But Hubble’s success in seeing water—by scrutinizing the pattern of light coming from the planets and looking for distinct gaps where certain wavelengths are absorbed by water—paves the way to spotting it in more hospitable worlds.

14. Uncovering black holes

Today the idea of black holes seems like a given, but for a long time they existed only in theory. It wasn’t until 1994 that Hubble provided evidence for a massive black hole, the size of our solar system but weighing the same as about 3 billion suns, at the center of the galaxy M87. The telltale evidence lay in Hubble’s observations of the pancake-like disk of gas near M87’s center, which swirls at phenomenal speed around the black hole.

15. Courtside seats to galactic mergers

Four billion years from now, it’s thought, the Milky Way and the Andromeda Galaxy are going to collide. We probably won’t get to see it, since the Earth’s water will all have boiled off by our expanding sun, but it should be something to behold. As it turns out, though, galactic mergers are far from rare. A 2009 analysis of Hubble data shows that almost every galaxy has merged with another at least once since the early days of the universe. And those mergers might play a role in star formation.

16. Finding extra moons of Pluto

Pluto’s moon Charon was discovered long before Hubble took to space, but the telescope has helped uncover four other companions of the dwarf planet: Nix and Hydra, found in 2005, and Kerberos and Styx, discovered in 2011 and 2012.

17. Predicting the end of the universe

Not only can Hubble data be used to predict the birth of the universe, it can also provide an estimate of its death. In 2004, a team led by Stanford astrophysicist Andrei Linde used observations of fast-moving supernovae to calculate that the universe has about 24 billion more years before time runs out. Just how that end occurs—with a bang, a whimper, or infinite expansion into nothingness—is less clear.

18. Mapping dark matter

We can’t see dark matter directly, but Hubble allows us to infer its location. The galaxy cluster Abell 1689 is one of the best tools scientists have for this. The cluster, located 2.2 billion light years from Earth, contains dense concentrations of dark matter that distort the light coming from behind Abell 1689.

19. Characterizing the Kuiper Belt

In 2009, Hubble was able to spot the smallest object in the Kuiper Belt ever seen. The icy little body, just 3,200 feet across and orbiting 4.2 billion miles from Earth, was spotted almost by accident, when it passed in front of a guide star that Hubble was using to orient itself.

20. What causes short gamma ray bursts?

Short gamma ray bursts have long been a puzzle for astronomers; they couldn’t figure out just where these occasional flashes of intense radiation came from. Then, in June 2013, Hubble scrutinized one such burst initially spotted by NASA’s Swift space telescope. Tracking the burst back to its source revealed that the culprit was two small dense stellar objects that crashed together.

21. Spotting renegade stars

Some stars, it turns out, can go rogue. Hubble spotted 14 such stellar runaways rushing through the interstellar medium at more than 112,000 miles per hour, kicking up bright, arrow-shaped streams as their stellar winds collide with the gas of the medium.

22. Smallest solar system?

A tiny brown dwarf star known poetically as Cha 110913-773444 may turn out to be the center of the smallest solar system yet discovered. The star is just eight times as massive as Jupiter, but the Hubble and Spitzer telescopes spotted what looks like a disk of dust around it that could eventually coalesce into planets.

23. A witness to the deaths of stars

A star’s death is one of the most beautiful tragedies in reality—and the grand finale, as the star sheds outer layers of gas that bloom in a fabulous cocoon, makes for some of Hubble’s most beautiful images.

24. Watching planets form—and die

In the Orion Nebula, planetary formation is like “constructing a skyscraper in the middle of a tornado,” according to NASA. Hubble’s view of the early planetary building blocks in the nebula shows how hard it can be for these satellites to form as they’re blasted by ultraviolet radiation.

25. Finding precursors for alien life

In 2008, Hubble detected an organic molecule in the atmosphere of an alien world for the first time. While the planet, circling a star in the constellation Vulpeca, is too hot for life as we know it to thrive, the methane found in its atmosphere is thought to play a role in the chemical reactions that could eventually result in life.


Image: NASA


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