Neutron Star Collision Cooks Up Exotic Elements, Gravitational Waves
When some people get in the kitchen, they create a delicious meal but leave behind a chaotic mess of splattered food and dirty dishes. Cosmic cookery can be just as messy. While a star can create chemical elements as heavy as iron within its core, anything heavier needs a more powerful source like a stellar explosion or the collision of two neutron stars.
Colliding neutron stars can yield gold, plutonium, and a variety of other elements. Theoretically, they also generate gravitational waves as they spiral together at breakneck speed before merging. The first gravitational wave signal from a neutron star merger was detected on August 17. It was accompanied by gamma rays and other light, allowing astronomers to locate a gravitational wave source for the first time.
Hubble photographed the glow from this titanic collision, shining within the galaxy NGC 4993 at a distance of 130 million light-years. Hubble also obtained an infrared spectrum that may yield signs of exotic, radioactive elements. The analysis will continue while astronomers wait for the gravitational wave source to emerge from behind the Sun from Earth’s point of view, where it slipped just days after discovery.
The Comet that Came in from the Cold
A solitary frozen traveler has been journeying for millions of years toward the heart of our planetary system. The wayward vagabond, a city-sized snowball of ice and dust called a comet, was gravitationally kicked out of the Oort Cloud, its frigid home at the outskirts of the solar system. This region is a vast comet storehouse, composed of icy leftover building blocks from the construction of the planets 4.6 billion years ago.
The comet is so small, faint, and far away that it eluded detection. Finally, in May 2017, astronomers using the Panoramic Survey Telescope and Rapid Response System (Pan-STARRS) in Hawaii spotted the solitary intruder at a whopping 1.5 billion miles away — between the orbits of Saturn and Uranus. The Hubble Space Telescope was enlisted to take close-up views of the comet, called C/2017 K2 PANSTARRS (K2).
The comet is record-breaking because it is already becoming active under the feeble glow of the distant Sun. Astronomers have never seen an active inbound comet this far out, where sunlight is merely 1/225th its brightness as seen from Earth. Temperatures, correspondingly, are at a minus 440 degrees Fahrenheit. Even at such bone-chilling temperatures, a mix of ancient ices on the surface — oxygen, nitrogen, carbon dioxide, and carbon monoxide — is beginning to sublimate and shed as dust. This material balloons into a vast 80,000-mile-wide halo of dust, called a coma, enveloping the solid nucleus.
Astronomers will continue to study K2 as it travels into the inner solar system, making its closest approach to the Sun in 2022.
An Asteroid That Split in Two 5,000 Years Ago Is Spouting a Comet Tail
Astronomers categorize the minor bodies in the solar system according to their location and physical composition. Comets are a loose collection of ice and dust that fall in toward the Sun from beyond the orbits of the major planets, and grow long tails of dust and gas along the way. Asteroids are rocky or metallic and are relegated to a zone between Mars and Jupiter. But nature isn't that tidy. The Hubble Space Telescope photographed a pair of asteroids orbiting each other that have a tail of dust, which is definitely a comet-like feature. The odd object, called 2006 VW139/288P, is the first known binary asteroid that is also classified as a main-belt comet. Roughly 5,000 years ago, 2006 VW139/288P probably broke into two pieces due to a fast rotation.
Alien world traps most of the visible light falling into its atmosphere
Don't go looking for the proverbial black cat eating licorice in a coal bin on the planet WASP-12b. Twice the size of any planet found in our solar system, the world is as black as fresh asphalt. Unlike other planets in its class, WASP-12b has the unique capability to trap at least 94 percent of the visible starlight falling into its atmosphere.
The temperature of the atmosphere is a seething 4,600 degrees Fahrenheit, which prevents the formation of reflective clouds on the day side. The planet orbits so close to its host that it is tidally locked, which means that it keeps the same side always facing the star.
The exoplanet isn't dining alone. Its host star is also having a feast: gobbling up material swirling off the exoplanet's super-heated atmosphere.
This oddball exoplanet is one of a class of so-called "hot Jupiters" that orbit very close to their host star and are heated to extreme temperatures. WASP-12b circles a Sun-like star 1,400 light-years from Earth.
Scorching "Hot Jupiter" Has a Stratospheric Layer
Only when we fly in a commercial jet at an altitude of about 33,000 feet do we enter Earth's stratosphere, a cloudless layer of our atmosphere that blocks ultraviolet light. Astronomers were fascinated to find evidence for a stratosphere on a planet orbiting another star. As on Earth, the planet's stratosphere is a layer where temperatures increase with higher altitudes, rather than decrease. However, the planet (WASP-121b) is anything but Earth-like. The Jupiter-sized planet is so close to its parent star that the top of the atmosphere is heated to a blazing 4,600 degrees Fahrenheit (2,500 degrees Celsius), hot enough to rain molten iron! This new Hubble Space Telescope observation allows astronomers to compare processes in exoplanet atmospheres with the same processes that happen under different sets of conditions in our own solar system.