We live in a gigantic star city. Our Milky Way galaxy contains an estimated 200 billion stars. But that's just the bare tip of the iceberg. The Milky Way is surrounded by vast amounts of an unknown material called dark matter that is invisible because it doesn't release any radiation. Astronomers know it exists because, dynamically, the galaxy would fly apart if dark matter didn't keep a gravitational lid on things.

Still, astronomers would like to have a precise measure of the galaxy's mass to better understand how the myriad galaxies throughout the universe form and evolve. Other galaxies can... Read more

In nabbing exoplanets that are precariously close to their stars, astronomers have discovered a shortage of one type of alien world. It's a predicted class of Neptune-sized world that orbits just a few million miles from its star, much closer than the 93-million-mile distance between Earth and the Sun. Dubbed "hot Neptunes," these planets would have atmospheres that are heated to more than 1,700 degrees Fahrenheit (hot enough to melt silver).

However, the mysterious hot-Neptune deficiency suggests that these planets are rare, or, they were plentiful at one time, but have since disappeared. In... Read more

The explosive end to a massive star's life is one of the most powerful blasts in the universe. The material expelled by the violent stellar death enriches our galaxy with heavier elements, the building blocks of new stars and even planetary systems. Astronomers have diligently searched for the doomed progenitor stars in pre-explosion images. Studying these stars could help them in their quest to better understand stellar evolution.

Their quest has turned up a few pre-supernova stars. But the doomed stars for one class of supernova have eluded discovery: the hefty stars that explode as Type Ic... Read more

The term "HAZMAT" connotes danger. In this case, it's on a cosmic scale, where violent flares of seething gas from small, young stars may make entire planets uninhabitable. NASA's Hubble Space Telescope is observing such stars through a large program called HAZMAT — HAbitable Zones and M dwarf Activity across Time. This is an ultraviolet survey of red dwarfs — referred to as "M dwarfs" in astronomical circles — at three different ages: young, intermediate, and old.

Approximately three-quarters of the stars in our galaxy are red dwarfs. Most of the galaxy's "habitable-zone" planets orbit these... Read more

It takes more than a massive outburst to destroy the mammoth star Eta Carinae, one of the brightest known stars in the Milky Way galaxy. About 170 years ago, Eta Carinae erupted, unleashing almost as much energy as a standard supernova explosion.

Yet that powerful blast wasn’t enough to obliterate the star, and astronomers have been searching for clues to explain the outburst ever since. Although they cannot travel back to the mid-1800s to witness the actual eruption, they can watch a rebroadcast of part of the event — courtesy of some wayward light from the explosion. Rather than heading straight... Read more

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.