Astronomers from Germany and Turkey have analyzed available data from various space telescopes to investigate an ultraluminous X-ray source designated X-4, which is located in the nearby galaxy NGC 4631. Results of the new study, published June 22 on the preprint server arXiv, yield important insights into the spectral and timing variability of this source.

Ultraluminous X-ray sources (ULXs) are point sources in the sky that are so bright in X-rays that each emits more radiation than a million suns emit at all wavelengths. They are less luminous than active galactic nuclei but more consistently luminous than any known stellar process. Although numerous studies of ULXs have been conducted, the basic nature of these sources remains unknown.

Controversial claim challenges principle of cosmological sameness on which prevailing theory rests

The Gaia mission has allowed researchers to understand the motions of stars like never before, even revealing possible interactions between our solar system and nearby stars. Planetary Science Institute Senior Scientist Nathan Kaib and collaborator Sean Raymond (Universite de Bordeaux) have found that a recent stellar passage likely triggered a huge increase in comet formation as the star’s gravity altered Oort cloud objects’ orbits, sending them cascading into the inner solar system. We may even still be feeling the effects of this passage today. This work is being presented at the American Astronomical Society Division on Dynamical Astronomy.

HD 7,977 is a nearby sun-like star in the constellation Cassiopeia whose close passage was discovered by the Gaia mission. Approximately 2.5 million years ago, the orbits of the sun and HD 7,977 brought the two stars close together, but exactly how close is still an open question. Gaia data suggest they passed within 4,000–25,000 astronomical units of one another. Now, Kaib and Raymond have shown that the orbits of long-period comets suggest HD 7,977 came within 6,000–10,000 AU of our sun, setting off a major shower of new comets into the inner solar system.

Massive stars much bigger than our sun always come in pairs or groups, not alone. But astronomers don’t fully understand how these groupings form. In a new study, astronomers using ALMA have serendipitously discovered a young system containing nine baby stars forming together, and they have detailed a rare glimpse of the formation of such a stellar family in its earliest assembly stage in a paper submitted to the arXiv preprint server on June 2.

There are a few competing theories of how groups of stars form: disk, core and filament fragmentation. That is, a spinning disk of gas around a young star breaks apart into multiple pieces, or a big core of gas fragments into multiple star-forming clumps before the stars even form, or a long filamentary cloud of gas breaks into clumps along its length, each clump forming a star.

Massive stars, growing together as a group, are hard to study because they are far away, buried in thick dust and grow up fast while still in dense clouds. So astronomers have not caught many of them “in the act” of forming.