The Large and Small Magellanic Clouds are well known satellite galaxies of the Milky Way but there are more. It is surrounded by at least 61 within 1.4 million light years (for context the Andromeda Galaxy is 2.5 million light years away) but there are likely to be more. A team of astronomers have been hunting for more companions using the Subaru telescope and so far, have searched just 3% of the sky. To everyone’s surprise they have found nine previously undiscovered satellite galaxies, far more than expected.  Data from Gaia (the satellite collecting accurate position information of astronomical objects) suggests that most of the satellite galaxies orbiting our own are newcomers! Even the Large and Small Magellanic Clouds are now known to be newcomers. Whether any of these will fall into orbit around the Milky Way is as yet unknown, largely because we do not have an accurate measure for the mass of our home Galaxy. The recent search hopes to expand our understanding of this corner of the Universe with the first detailed search for companion dwarf galaxies. The paper from lead author Daisuke Homma and team from the National Astronomical Observatory of Japan reports on the findings of their survey using the Subaru Telescope.  Based on Mauna Kea in Hawaii The Subaru Telescope is an 8.2m diameter telescope located at the Mauna Kea Observatory in Hawaii. Until 2005 it was the largest single mirror telescope in the world with a gigantic 8.2 metre mirror. In all telescopes, larger mirrors collect more light bringing with it the ability to see fainter objects and finer levels of detail. A number of telescopes have now surpassed Subaru’s massive light collecting power but multi-mirror telescopes are becoming more popular.  As the cornerstone of the study is a drive to understand dark matter distribution. The concept of the Universe being dominated by cold dark matter nicely describes the large scale model of the cosmos. It struggles however, to describe the structure in the local Universe predicting hundreds of satellite galaxies to the Milky Way. Until recently, we only knew of a handful of satellite galaxies contradicting the model in a quandary known as the missing satellites problem. The team from Japan hopes their work will help provide clues to understand this problem. The paper reports that the previous data obtained before 2018 of an area of sky covering 676 degrees2 revealed three candidate satellite galaxies; Vir I, Cet III and Boo IV. Data released over the three years that followed covering 1,140 degrees2 revealed two additional candidates; Sext II and Vir III. Unexpectedly, the model suggests there should be  3.9 ± 0.9 satellite galaxies within 10 pc within the virial radius of the Milky Way (based on the density distribution of the Milky Way). Instead the team found more, nine to be precise! It seemed then that the missing satellite problem was no worse than expected, indeed there were too many galaxies! The team acknowledged that their research was based on statistically small numbers and several assumptions had been made based on an isotropic distribution of satellites. To progress this further, there will need to be follow up studies of stars in the satellite galaxies and high resolution imaging. Source : Final Results of Search for New Milky Way Satellites in the Hyper Suprime-Cam Subaru Strategic Program Survey: Discovery of Two More Candidates The post Does the Milky Way Have Too Many Satellite Galaxies? appeared first on Universe Today.

Exoplanets are a fascinating astronomy topic, especially the so-called “Hot Jupiters”. They’re overheated massive worlds often found orbiting very close to their stars—hence the name. Extreme gravitational interactions can tug them right into their stars over millions of years. However, some hot Jupiters appear to be spiraling in faster than gravity can explain. WASP-12b is a good example of one of these rapidly spiraling hot Jupiters. In about three million years, thanks to orbital decay, it will become one with its yellow dwarf host star. Both are part of a triple-star system containing two red dwarf stars. The hot Jupiter orbits the dwarf in just over one Earth day at a distance of about 3.5 million kilometers. That’s well within the orbit of Mercury around the Sun. Thanks to that orbit and gravitational influence, one side of the planet always faces the star. That heats only one side and puts the surface temperature at about 2,200 C. Eventually heat flows to the opposite side, which stirs up strong winds in the upper atmosphere. The planet doesn’t reflect much light, and astronomers have described it as a pitch-black world. As if all that isn’t odd enough, the gravitational pull of the nearby star distorts this hot Jupiter into an egglike shape. It’s also stripping the planet’s atmosphere away. So, it’s no wonder astronomers described WASP-12b as a doomed planet. Artist’s impression of WASP-12b, a Hot Jupiter deformed by its close orbit to its star. Credit: NASA What’s Tugging on Hot Jupiters? According to conventional theory, a hot Jupiter planet like WASP-12b should create strong gravitational tidal waves between themselves and their parent stars. Those waves transfer energy, which tugs at the planet. That pulls the planet right into the star. Such a fiery death is definitely in WASP-12b’s future. But, there’s just one problem: it’s getting sucked in faster than gravitational tidal waves can explain. What’s happening? A team of scientists at Durham University in England studied WASP-12b and they’ve come up with an interesting idea. What if this hot Jupiter’s fate is determined by magnetic fields? That’s what Durham’s Craig Duguid proposed in a recently published paper. Duguid’s team thinks the strong magnetic fields inside some stars can dissipate the tidal waves generated by orbiting hot Jupiters. Artist’s concept of the exoplanet WASP-12b, parent star devouring its hot Jupiter planet. Artwork Credit: NASA, ESA, and G. Bacon (STScI) How this works isn’t completely confirmed yet, but here’s the basic idea. Inwardly propagating internal gravity waves (IGWs) (such as those from the nearby hot Jupiter) move through a star. They eventually run into the star’s magnetic interior. If that magnetic field is strong enough, it transforms them into magnetic waves. They move back outward and eventually dissipate. In the process, however, that dissipation causes a huge energy drain. The result is still the same as with gravitational tidal waves: the hot Jupiter loses energy and plows into its parent star. And, it could explain why some hot Jupiters spiral into their stars more quickly than expected. Exploring the Magnetic Mechanism Idea In the paper, Duguid and his team used models of stars with convective cores—such as F-type stars with masses between 1.2 to 1.6 solar masses. Astronomers suspect these experience weak tidal dissipation. The team used the known properties of these stars’ interiors, along with estimates of their magnetic fields. For these stars, a convective core is the dynamo that generates the magnetic field. Although it’s classified as a type-G star, WASP-12 fits into the study, thanks to its near-solar mass and radius. So, is it just gravitational tidal waves pulling the planet in, or could the proposed magnetic field action be at work? Duguid and colleagues concluded that the magnetic field idea is very possible. They write, “Our main result is that this previously unexplored source of efficient tidal dissipation can operate in stars within this mass range for significant fractions of their lifetimes. This tidal dissipation mechanism appears to be consistent with the observed inspiral of WASP-12b and more generally could play an important role in the orbital evolution of hot Jupiters—and to lower-mass ultra-short-period planets—orbiting F-type stars.” Need More Data about Hot Jupiters It’s an interesting result. There are a great many hot Jupiters in the exoplanet archives, simply because they are the easiest exoplanets to observe. Some of them are spiraling in faster than expected. This leads the authors to suggest that additional studies of similar-type stars and their hot Jupiters could confirm the magnetic mechanism. In addition, future observations could help astronomers also understand the tidal wave theory and help place some constraints on the types of stars where it would operate. For More Information Scientists Explain Why Some Exoplanets are Spiraling Towards Their StarsAn Efficient Tidal Dissipation Mechanism via Stellar Magnetic Fields The post Why Hot Jupiters Spiral into Their Stars appeared first on Universe Today.

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