NASA Astronomy Picture of the Day

Dec 11 2022

Io in True Color

The strangest moon in the Solar System is bright yellow. The featured picture, an attempt to show how Io would appear in the "true colors" perceptible to the average human eye, was taken in 1999 July by the Galileo spacecraft that orbited Jupiter from 1995 to 2003. Io's colors derive from sulfur and molten silicate rock. The unusual surface of Io is kept very young by its system of active volcanoes. The intense tidal gravity of Jupiter stretches Io and damps wobbles caused by Jupiter's other Galilean moons. The resulting friction greatly heats Io's interior, causing molten rock to explode through the surface. Io's volcanoes are so active that they are effectively turning the whole moon inside out. Some of Io's volcanic lava is so hot it glows in the dark.

https://apod.nasa.gov/apod/astropix.html

Hubble Captures Dual Views of an Unusual Star Cluster

While these two images may look dazzlingly different, they are actually pictures of the same cosmic object: NGC 1850. Although the same Hubble instrument took both images, different filters with different assigned colors were used to study particular wavelengths of light emanating from these objects. The image with blue nebulosity includes some near-infrared light along with visible light (what our human eyes can detect), whereas the image with red nebulosity (also a different “pointing” at the same object) covers a much broader range from the near-ultraviolet to the beginnings of the infrared spectrum. Ultraviolet observations are ideal for detecting the light from the hottest and youngest stars, as seen in this luminous, starry view.

This 100 million-year-old globular cluster is located in the Large Magellanic Cloud, a satellite galaxy of the Milky Way and a birthplace for billions of stars. The cluster is approximately 160,000 light-years away in the constellation Dorado. Typical of globular clusters, it is a spherical collection of densely packed stars held together by mutual gravitational attraction. Unlike most globular clusters, however, the stars of NGC 1850 are relatively young. Globular clusters with young stars such as NGC 1850 are not present in our own Milky Way galaxy.

Astrophysicists theorize that when the first generation of stars in NGC 1850 was born, the stars ejected matter like dust and gas into the surrounding cosmos. The density of the newly formed star cluster was so high that this ejected matter could not escape the cluster’s gravitational pull, causing it to stay nearby. The intense gravity of the cluster also pulled in hydrogen and helium gas from its surroundings. These two sources of gas combined to form a second generation of stars, increasing the density and size of this globular cluster.

In 2021, scientists detected the presence of a black hole in NGC 1850. They have also detected many brighter blue stars (seen on the right of the second image) that burn hotter and die younger than red stars. Also present are around 200 red giants, stars that have run out of hydrogen in their centers and are fusing hydrogen further from their core, causing the outer layers to expand, cool, and glow red (seen throughout the second image). Surrounding the cluster is a pattern of nebulosity, diffuse dust and gas theorized to come from supernova blasts (the blue veil-like structures on the first image and the red ones on the second image).

NGC 1850 is approximately 63,000 times the mass of the Sun, and its core is roughly 20 light-years in diameter. Astronomers used Hubble Space Telescope observations at a wide range of wavelengths to image this large star cluster and learn more about star formation.

https://www.nasa.gov/image-feature/goddard/2022/hubble-captures-dual-views-of-an-unusual-star-cluster

Hubble Detects Ghostly Glow Surrounding Our Solar System

Aside from a tapestry of glittering stars, and the glow of the waxing and waning Moon, the nighttime sky looks inky black to the casual observer. But how dark is dark?

To find out, astronomers decided to sort through 200,000 images from NASA's Hubble Space Telescope and made tens of thousands of measurements on these images to look for any residual background glow in the sky, in an ambitious project called SKYSURF. This would be any leftover light after subtracting the glow from planets, stars, galaxies, and from dust in the plane of our solar system (called zodiacal light).

When researchers completed this inventory, they found an exceedingly tiny excess of light, equivalent to the steady glow of 10 fireflies spread across the entire sky. That's like turning out all the lights in a shuttered room and still finding an eerie glow coming from the walls, ceiling, and floor.

The researchers say that one possible explanation for this residual glow is that our inner solar system contains a tenuous sphere of dust from comets that are falling into the solar system from all directions, and that the glow is sunlight reflecting off this dust. If real, this dust shell could be a new addition to the known architecture of the solar system.

This idea is bolstered by the fact that in 2021 another team of astronomers used data from NASA's New Horizons spacecraft to also measure the sky background. New Horizons flew by Pluto in 2015, and a small Kuiper belt object in 2018, and is now heading into interstellar space. The New Horizons measurements were done at a distance of 4 billion to 5 billion miles from the Sun. This is well outside the realm of the planets and asteroids where there is no contamination from interplanetary dust.

New Horizons detected something a bit fainter that is apparently from a more distant source than Hubble detected. The source of the background light seen by New Horizons also remains unexplained. There are numerous theories ranging from the decay of dark matter to a huge unseen population of remote galaxies.

"If our analysis is correct there's another dust component between us and the distance where New Horizons made measurements. That means this is some kind of extra light coming from inside our solar system," said Tim Carleton, of Arizona State University (ASU).

"Because our measurement of residual light is higher than New Horizons we think it is a local phenomenon that is not from far outside the solar system. It may be a new element to the contents of the solar system that has been hypothesized but not quantitatively measured until now," said Carleton.

Hubble veteran astronomer Rogier Windhorst, also of ASU, first got the idea to assemble Hubble data to go looking for any "ghost light." "More than 95% of the photons in the images from Hubble's archive come from distances less than 3 billion miles from Earth. Since Hubble's very early days, most Hubble users have discarded these sky-photons, as they are interested in the faint discrete objects in Hubble's images such as stars and galaxies," said Windhorst. "But these sky-photons contain important information which can be extracted thanks to Hubble's unique ability to measure faint brightness levels to high precision over its three decades of lifetime."

A number of graduate and undergraduate students contributed to project SKYSURF, including Rosalia O'Brien, Delondrae Carter and Darby Kramer at ASU, Scott Tompkins at the University of Western Australia, Sarah Caddy at Macquarie University in Australia, and many others.

The team's research papers are published in The Astronomical Journal and The Astrophysical Journal Letters.

https://www.nasa.gov/feature/goddard/2022/hubble-detects-ghostly-glow-surrounding-our-solar-system

https://iopscience.iop.org/journal/2041-8205

Hubble Captures a Glittering Neighbor

This image from the NASA/ESA Hubble Space Telescope captures a small portion of the Small Magellanic Cloud (SMC). The SMC is a dwarf galaxy and one of the Milky Way’s nearest neighbors, lying only about 200,000 light-years from Earth. It makes a pair with the Large Magellanic Cloud, and both objects are best seen from the Southern Hemisphere, but are visible from some northern latitudes as well.

The Small Magellanic Cloud contains hundreds of millions of stars, but this image focuses on just a small fraction of them. These stars comprise the open cluster NGC 376, which has a total mass only about 3,400 times that of the Sun. Open clusters, as the name suggests, are loosely bound and sparsely populated. This distinguishes open clusters from globular clusters, which generally appear as a continuous blur of starlight at their centers because they are so crammed with stars. In the case of NGC 376, individual stars are clearly discernable even in the most densely populated parts of this image.

The data in this image come from two different astronomical investigations which relied on two of Hubble’s instruments: the Wide Field Camera 3 (WFC3) and the Advanced Camera for Surveys (ACS). The first investigation used the ACS to explore a handful of star clusters in the Small Magellanic Cloud and helped astronomers explore topics including the abundance of low- and high-mass stars in different environments. The second investigation used both the WFC3 and ACS, and aimed to answer fundamental questions about the lives of stars and help astronomers understand precisely where, when, why, and how stars form.

https://www.nasa.gov/image-feature/goddard/2022/hubble-captures-a-glittering-neighbor

>>17925384

So ultra thankful