Using the powerful Hubble and Gaia space telescopes, astronomers just took a big step toward finding the answer to the Hubble constant, one of the most important and long-sought numbers in all of cosmology. This number measures the rate at which the universe is expanding since the big bang, 13.8 billion years ago. The constant is named for astronomer Edwin Hubble, who nearly a century ago discovered that the universe was uniformly expanding in all directions. Now, researchers have calculated this number with unprecedented accuracy.

Intriguingly, the new results further intensify the discrepancy... Read more

Much of the light in the universe comes from stars, and yet, star formation is still a vexing question in astronomy.

To piece together a more complete picture of star birth, astronomers have used the Hubble Space Telescope to look at star formation among galaxies in our own cosmic back yard. The survey of 50 galaxies in the local universe, called the Legacy ExtraGalactic UV Survey (LEGUS), is the sharpest, most comprehensive ultraviolet-light look at nearby star-forming galaxies.

The LEGUS survey combines new Hubble observations with archival Hubble images for star-forming spiral and dwarf... Read more

In the fading afterglow of a supernova explosion, astronomers using NASA’s Hubble Space Telescope have photographed the first image of a surviving companion to a supernova. This is the most compelling evidence that some supernovas originate in double-star systems. The companion to supernova 2001ig’s progenitor star was no innocent bystander to the explosion—it siphoned off almost all of the hydrogen from the doomed star’s stellar envelope. SN 2001ig is categorized as a Type IIb stripped-envelope supernova, which is a relatively rare type of supernova in which most, but not all, of the hydrogen is... Read more

When you want to know the size of a room, you use a measuring tape to calculate its dimensions.

But you can’t use a tape measure to cover the inconceivably vast distances in space. And, until now, astronomers did not have an equally precise method to accurately measure distances to some of the oldest objects in our universe – ancient swarms of stars outside the disk of our galaxy called globular clusters.

Estimated distances to our Milky Way galaxy’s globular clusters were achieved by comparing the brightness and colors of stars to theoretical models and observations of local stars. But the... Read more

Through a quirk of nature called “gravitational lensing,” a natural lens in space amplified a very distant star’s light. Astronomers using Hubble took advantage of this phenomenon to pinpoint the faraway star and set a new distance record for the farthest individual star ever seen. They also used the distant star to test one theory of dark matter, and to probe the make-up of a galaxy cluster. The team dubbed the star “Icarus,” after the Greek mythological character who flew too near the Sun on wings of feathers and wax that melted. Its official name is MACS J1149+2223 Lensed Star 1.

Grand, majestic spiral galaxies like our Milky Way are hard to miss. Astronomers can spot these vast complexes because of their large, glowing centers and their signature winding arms of gas and dust, where thousands of glowing stars reside.

But some galaxies aren't so distinctive. They are big, but they have so few stars for their size that they appear very faint and diffuse. In fact, they are so diffuse that they look like giant cotton balls.

Observations by NASA's Hubble Space Telescope of one such galaxy have turned up an oddity that sets it apart from most other galaxies, even the... Read more

The universe is so huge that it's estimated that a star explodes as a supernova once every second. Astronomers capture a small fraction of these detonations because they are comparatively short-lived, like fireflies flickering on a summer evening. After skyrocketing to a sudden peak in brightness, a supernova can take weeks to slowly fade away.

For the past decade astronomers have been befuddled by a more curious "flash-in-the-pan" that pops up and then disappears in just a few days, not weeks. It's called a Fast-Evolving Luminous Transient (FELT). Only a few FELTs have been seen in telescopic sky... Read more

The adventuring cinema archeologist Indiana Jones would be delighted to find a long-sought relic in his own backyard. Astronomers have gotten lucky enough to achieve such a quest. They identified a very rare and odd assemblage of stars that has remained essentially unchanged for the past 10 billion years. The diffuse stellar island provides valuable new insights into the origin and evolution of galaxies billions of years ago.

As far as galaxy evolution goes, this object is clearly a case of “arrested development.” The galaxy, NGC 1277, started its life with a bang long ago, ferociously churning... Read more

Finding lots of dust around stars may not sound like anything astronomers would get excited about. The universe is a dusty place. But dust around a young star can be evidence that planet formation is taking place. This isn’t a new idea. In 1755, German Philosopher Immanuel Kant first proposed that planets formed around our Sun in a debris disk of gas and dust. Astronomers imagined that this process might take place around other stars.

They had to wait until the early 1980s for the first observational evidence for a debris disk around any star to be uncovered. An edge-on debris disk was... Read more

The good news: Astronomers have made the most precise measurement to date of the rate at which the universe is expanding since the big bang. The possibly unsettling news: This may mean that there is something unknown about the makeup of the universe. The new numbers remain at odds with independent measurements of the early universe's expansion. Is something unpredicted going on in the depths of space?

Astronomers have come a long way since the early 1900s when they didn't have a clue that we lived in an expanding universe. Before this could be realized, astronomers needed an accurate celestial... Read more