Next Week’s Night Sky:
At 19:05 GMT on Thursday, Feb. 11, the moon will officially reach its new moon phase. While new, the moon is travelling between Earth and the sun. Since sunlight can only reach the far side of the moon, and the moon is in the same region of the sky as the sun, the moon becomes completely hidden from view for about a day. After the new moon Earth’s celestial night-light will return to shine in the western evening sky.
A Black Widow Pulsar
Using the computing power of the citizen-science project Einstein@Home to analyse data from NASA’s Fermi Space Telescope, researchers have identified a rapidly spinning pulsar, a so-called “black widow,” that is slowly but surely evaporating a companion star.
PSR J2039-5617 was a known source of X-rays and gamma rays and astronomers suspected the presence of a pulsar in a binary system. But evidence to confirm that proved difficult.
As it turns out, the pulsar is slowly destroying the companion star, which is about one-sixth as massive as the Sun. The two complete one orbit of each other every 5.5 hours and the brightness of the companion varies depending on where it is in the orbit.
For J2039-5617, there are two main processes at work: The pulsar heats up one side of the light-weight companion, which appears brighter and bluish. Additionally, the companion is distorted by the pulsar’s gravitational pull causing the apparent size of the star to vary over the orbit.
A Milky Way collision
When most of us picture the shape of the Milky Way, the galaxy that contains our own sun and hundreds of billions of other stars, we think of a central mass surrounded by a flat disc of stars that spiral around it. However, astronomers know that rather than being symmetrical, the disc structure is warped, more like the brim of a fedora, and that the warped edges are constantly moving around the outer rim of the galaxy.
What caused that warp to occur has been the subject of debate. Some researchers suggest that the phenomenon is a result of the instability of the galaxy itself, while others assert that it is the remnant of a collision with another galaxy in the distant past.
Using data from the Gaia space observatory, a satellite launched in 2013 by the European Space Agency to measure the positions, distances and motions of billions of stars and information from APOGEE, an infrared spectrograph developed by UVA to examine the chemical composition and motions of stars, astronomers now have the tools to observe the movements of the stars in the Milky Way with an unprecedented degree of accuracy.
Using that data, researchers have developed a model that characterizes the parameters of the galactic warp, where it begins in the outer disk, how fast the warp is moving and the shape of the warp. The model has helped them determine that the warp, which doesn’t affect our own sun, but is passing our solar system now at speeds that allow it to make a full rotation around the galaxy every 450 million years, is not a result of the Milky Way’s own internal mass. Instead, it is the relic of gravitational tugging on the Milky Way’s disk by the nearby passage of a satellite galaxy, possibly the Sagittarius Dwarf Spheroidal Galaxy, about 3 billion years ago.
To learn more, go here: https://iopscience.iop.org/article/10.3847/1538-4357/abc3c2
Gravitational Lensing
A research team with participation by Berkeley Lab physicists has used artificial intelligence to identify more than 1,200 possible gravitational lenses—objects that can be powerful markers for the distribution of dark matter. The count, if all of the candidates turn out to be lenses, would more than double the number of known gravitational lenses.
Gravitational lenses result from large celestial objects, like galaxies or galaxy clusters, that bend the path of light traveling from more distant galaxies. When these chance alignments are almost perfect, this creates false images that can include rings, partial rings, multiple images, and other illusions.
The lenses can tell us about the contribution of dark matter in those distant, lensed objects, as we can only witness dark matter through its gravitational effects on visible matter. And that could help unravel one of the biggest mysteries in the universe, as dark matter accounts for an estimated 85% of the total mass of the universe.
Researchers used a sample of 632 observed lenses and lens candidates, and 21,000 non-lenses to train the deep neural networks used in the study. The sample set was obtained from two sky surveys: the Dark Energy Camera Legacy Survey (DECaLS) and Dark Energy Survey (DES). About one in 10,000 massive galaxies was expected to be a strong gravitational lensing candidate.
The DECaLS survey was one of three surveys that was conducted in preparation for the startup of the Dark Energy Spectroscopic Instrument (DESI), a Berkeley Lab-led experiment that will help us to better understand dark energy, which is driving the universe apart at an accelerating rate.
To learn more, go here: https://arxiv.org/abs/2005.04730
Do you have any cool astronomy research news from this week? Share it in the comments below!