The old adage "what goes up must come down" even applies to an
immense cloud of hydrogen gas outside our Milky Way galaxy. First
discovered in the 1960s, the comet-shaped cloud is 11,000 light-years
long and 2,500 light-years across. If the cloud could be seen in visible
light, it would span the sky with an apparent diameter 30 times greater
than the size of the full moon. The cloud, which is invisible at optical wavelengths, is plummeting toward our galaxy at nearly
700,000 miles per hour. Hubble was used to measure the chemical
composition of the cloud as a means of assessing where it came from.
Hubble astronomers were surprised to find that the cloud, which is
largely composed of hydrogen, also has heavier elements that could only
come from stars. This means the cloud came from the star-rich disk of
our galaxy. The Smith Cloud is following a ballistic trajectory and will plow
back into the Milky Way's disk in about 30 million years. When it does,
astronomers believe it will ignite a spectacular burst of star formation,
perhaps providing enough gas to make 2 million suns.
Please join the scientists in a live discussion about the origin and conclusions of this research during the Hubble Hangout at 3pm EST today (Thurs., Jan. 28, 2016): http://hbbl.us/Baq .
Stellar astrophysics: The mystery of globular clusters
Nature 529, 7587 (2016). doi:10.1038/529473a
Authors: Antonella Nota & Corinne Charbonnel
The discovery of multiple stellar populations — formed at different times — in several young star clusters adds to the debate on the nature and origin of such populations in globular clusters from the early Universe. See Letter p.502
Formation of new stellar populations from gas accreted by massive young star clusters
Nature 529, 7587 (2016). doi:10.1038/nature16493
Authors: Chengyuan Li, Richard de Grijs, Licai Deng, Aaron M. Geller, Yu Xin, Yi Hu & Claude-André Faucher-Giguère
Stars in clusters are thought to form in a single burst from a common progenitor cloud of molecular gas. However, massive, old ‘globular’ clusters—those with ages greater than ten billion years and masses several hundred thousand times that of the Sun—often harbour multiple stellar populations, indicating that more than one star-forming event occurred during their lifetimes. Colliding stellar winds from late-stage, asymptotic-giant-branch stars are often suggested to be triggers of second-generation star formation. For this to occur, the initial cluster masses need to be greater than a few million solar masses. Here we report observations of three massive relatively young star clusters (1–2 billion years old) in the Magellanic Clouds that show clear evidence of burst-like star formation that occurred a few hundred million years after their initial formation era. We show that such clusters could have accreted sufficient gas to form new stars if they had orbited in their host galaxies’ gaseous disks throughout the period between their initial formation and the more recent bursts of star formation. This process may eventually give rise to the ubiquitous multiple stellar populations in globular clusters.
Hawking’s latest black-hole paper splits physicists
Nature 529, 7587 (2016). http://www.nature.com/doifinder/10.1038/529448a
Author: Davide Castelvecchi
Some welcome his latest report as a fresh way to solve a black-hole conundrum; others are unsure of its merits.
Astronomy: Turbulence roils luminous galaxy
Nature 529, 7587 (2016). doi:10.1038/529440c
The brightest-known galaxy is blasting gas out into space — and providing astronomers with a rare glimpse of how extreme galaxies evolve.Known as W2246-0526, the galaxy is as bright as 350 trillion Suns and is powered by a supermassive black hole at its heart.
Some of the Milky Way's "celebrity stars" opulent, attention-getting, and short-lived can be found in this Hubble Space Telescope image of the glittering star cluster called Trumpler 14. It is located 8,000 light-years away in the Carina Nebula, a huge star-formation region in our galaxy. Because the cluster is only 500,000 years old, it has one of the highest concentrations of massive, luminous stars in the entire Milky Way. Like some Hollywood celebrities, the stars will go out in a flash. Within just a few million years they will burn out and explode as supernovae. But the story's not over. The blast waves will trigger the formation of a new generation of stars inside the nebula in an ongoing cycle of star birth and death.
A prevalence of dynamo-generated magnetic fields in the cores of intermediate-mass stars
Nature 529, 7586 (2016). doi:10.1038/nature16171
Authors: Dennis Stello, Matteo Cantiello, Jim Fuller, Daniel Huber, Rafael A. García, Timothy R. Bedding, Lars Bildsten & Victor Silva Aguirre
Magnetic fields play a part in almost all stages of stellar evolution. Most low-mass stars, including the Sun, show surface fields that are generated by dynamo processes in their convective envelopes. Intermediate-mass stars do not have deep convective envelopes, although 10 per cent exhibit strong surface fields that are presumed to be residuals from the star formation process. These stars do have convective cores that might produce internal magnetic fields, and these fields might survive into later stages of stellar evolution, but information has been limited by our inability to measure the fields below the stellar surface. Here we report the strength of dipolar oscillation modes for a sample of 3,600 red giant stars. About 20 per cent of our sample show mode suppression, by strong magnetic fields in the cores, but this fraction is a strong function of mass. Strong core fields occur only in red giants heavier than 1.1 solar masses, and the occurrence rate is at least 50 per cent for intermediate-mass stars (1.6–2.0 solar masses), indicating that powerful dynamos were very common in the previously convective cores of these stars.