Hubble turns 26 on April 24, 2016, approaching three decades of unveiling incredible mysteries in the universe. The James Webb Space Telescope, Hubble's successor, is scheduled to launch in 2018, but Hubble could last beyond 2030.
Until then, here's a look at some of the discoveries Hubble has made:
All images courtesy NASA Hubble Space Telescope
Galaxy UGC 477 is just over 110 million light years away in the constellation Pisces (The Fish), but it's a difficult find because it's so dim – a low surface brightness (LSB) galaxy up to 250 times fainter than the night sky.
The European Space Agency reports that LSB galaxies are made mostly of hydrogen gas instead of stars, and their centers don't bulge out with a large mass of stars. Scientists think this is because they are so remote from neighboring galaxies and haven't had galactic collisions to kick-start star formation.
Another compelling thing about LSB galaxies is that they appear to contain lots of dark matter, "making them excellent objects to study" to help learn about this mysterious substance.
Looking into the heart of our Milky Way galaxy, Hubble finds a dense collection of more than 500,000 stars – the most massive and densest star cluster in the galaxy. They're packed so closely that "it is equivalent to having a million suns crammed into the volume of space between us and our closest stellar neighbor, Alpha Centauri, 4.3 light-years away." The cluster surrounds the Milky Way's central supermassive black hole, which is about 4 million times the mass of our sun. Hubble captured this image in infrared to see through galactic dust that obscures the star cluster's visible light. Astronomers then translated the infrared light into colors our eyes can see. Some dust was so thick, even infrared can't penetrate it, and they show up as dark silhouettes against the brighter stars. Scientists estimate about 10 million stars are too faint to show in this mosaic of nine Hubble images spanning a total distance of 50 light years.
An ultraviolet survey made possible thanks to an upgrade by the Shuttle Atlantis crew in May 2009 has provided astronomers an opportunity to study star cluster R136. It's in the Tarantula Nebula within the Large Magellanic Cloud about 170,000 light years from Earth. Relatively small but home to dozens of massive stars – including the most massive star ever found – Hubble imagery has revealed nine stars in the cluster that are more than 100 times bigger than our sun. Four of them are at least 150 times the sun's mass.
First discovered by Scottish astronomer Williamina Fleming in 1888, this view of the Horsehead Nebula was captured by Hubble 125 years later. Fleming developed a classification system for stars based on the amount of hydrogen in their composition. This method was later expanded upon by American astronomer Annie Jump Cannon who separated the stars into spectral classes O, B, A, F, G, K, M. She developed a mnemonic, "Oh Be a Fine Girl, Kiss Me" as a way to remember the classifications.
Astronomers have long pondered the origins of this long ribbon of gas that stretches halfway around the Milky Way galaxy. Hubble delivered the answer in 2015, showing that two dwarf galaxies – the Large and Small Magellanic Clouds – orbiting the Milky Way are the source of this gaseous stream.
IRAS 12196-6300, a star just under 10 million years old, is still in its infancy. Unlike the sun, it's not yet burning hydrogen at its core. Further evidence of its youth is seen by the presence of reflection nebulae, the hazy clouds seen floating above and below it, which are created when light from a star reflects off a high concentration of nearby dust.
What do you get when you take two reasonable-sized galaxies and slam them together? You get a giant elliptical galaxy like NGC 3597, which is in the constellation of Crater (The Cup) about 150 million light-years away from Earth.
The remnants of a supernova, the Veil Nebula exploded roughly 8,000 years ago. The nebula stretches 110 light-years across approximately 2,100 light-years away in the constellation Cygnus – the Swan.
The Monkey Head Nebula is a cluster of young stars embedded in bright wisps of cosmic gas and dust within the constellation Orion (the Hunter) 6,400 light-years from Earth.
When the Smith Cloud began its remarkable journey toward us 70 million years ago, no one was around to notice it. Astronomers expect the cloud to collide with the Milky Way some 30 million years from now, birthing a mass of stars from enough gas to make 2 million.
Known as NGC 6503, this dwarf spiral galaxy sits all alone in a region of otherwise empty space known as the Local Void, which is about 150 million light-years across.
Hubble got a dramatic look at the Southern Pinwheel Galaxy, which is made of bright stars and thick dust 15 million light-years away in the constellation of Hydra, the Sea Serpent. If you know where to look and have a pair of binoculars, you can see it from Earth.