In previous research on dark matter stars, it has often been assumed that stars accreting dark matter will continue to grow until they become so dense that they collapse into black holes. However, in the new study the physicists’ simulations showed that these stars actually appear to be stable and do not become black holes. Their stability arises from a self-regulatory mechanism called “gravitational cooling” in which the stars eject mass to slow down and stop their growth before they approach the critical Chandrasekhar limit, the point at which they collapse into black holes. As the scientists explain, the finding that dark matter stars are stable makes a surprising contribution to the research in this area.”Although it was known for some time that dark matter can be accreted by stars and form dark matter cores at their center, those studies were all phenomenological,” Brito said. “In addition, basically all these studies suggested that, if enough dark matter is accreted by a star, it will eventually trigger gravitational collapse and a black hole would form, eventually eating all the star.”We set about checking these claims, using a rigorous fully relativistic framework, i.e., solving the full Einstein’s equations. This is important if we want to understand how the dark matter core behaves for large densities. Well, it turns out that our results show that black hole formation can, in principle, be avoided by ejecting excessive mass: the dark matter core starts ‘repelling’ itself when it is too massive and compact, and is unable to grow past a certain threshold. This is, as far as we know, something that was ignored in previous works. “The above results are quite generic. Because any self-gravitating massive bosonic field can form compact structures, any such putative dark matter component would lead to the kind of effects we discuss in our paper. In this sense it proposes another way to search for these kinds of particles that can be complementary to observations coming from cosmology, for example. Given the lack of information that we have about the nature of dark matter, we think that it might be worth the effort to further develop this subject.”The scientists hope that the results here may help guide future research by suggesting where to look for dark matter and what methods to use to detect it.”We don’t know much about dark matter,” Brito said. “The only thing we do know is that all kinds of matter (be it regular matter or dark, invisible matter) fall in the same way in gravitational fields. This is Einstein’s equivalence principle in action. Thus, dark matter also falls in the usual way. It seems therefore appropriate to look for effects of dark matter in regions where gravity is strong, like neutron stars, black holes, etc. We are now trying to understand how dark matter behaves generically in regions of strong gravity.”At this precise moment, we are working on a long version of this letter. We want to understand in depth how the dark matter core grows for different kind of scenarios, and how viscosity in the star’s material affects the development of the accretion process.” (Phys.org)—Dark matter has never been seen directly, but scientists know that something massive is out there due to its gravitational effects on visible matter. One explanation for how such a large amount of mass appears to be right in front of our eyes yet completely invisible by conventional means is that the dark matter is hiding in the centers of stars. This sequence shows snapshots of a star’s density when two dark matter cores collide, where the x-axis is the plane of collision (only half the space is shown, but the remaining space can be obtained by symmetry). Although the final configuration is more compact and massive than the original, the star does not collapse into a black hole because it ejects some of its mass, slowing down its growth so that it remains stable. Credit: Brito, et al. ©2015 American Physical Society Dark matter guides growth of supermassive black holes In a new study, physicists have investigated the possibility that large amounts of hidden mass inside stars might be composed of extremely lightweight hypothetical particles called axions, which are a primary dark matter candidate. The scientists, Richard Brito at the University of Lisbon in Portugal; Vitor Cardoso at the University of Lisbon and the Perimeter Institute for Theoretical Physics in Waterloo, Ontario, Canada; and Hirotada Okawa at Kyoto University and Waseda University, both in Japan, have published their paper on dark matter in stars in a recent issue of Physical Review Letters.”Our work studies how dark matter piles up inside stars if the dark matter is composed of massive bosonic particles (axions are an example of such particles),” Brito told Phys.org. “Our results show that dark matter accretion by stars does not lead to gravitational collapse; instead it may give rise to characteristic vibrations in stars.” The researchers theoretically showed that, if numerous axions were to pile up inside normal stars, then the dark matter core would oscillate. The oscillating core would in turn cause the star’s fluid to oscillate in tune with it at a specific frequency related to the star’s mass, or at multiples of this frequency. For a typical axion mass, the oscillating stars would emit microwave radiation and might have observable effects.”What oscillates is the fluid density and its pressure, but it’s probably correct as well to say that the entire star is oscillating,” Brito explained. “These are like sound waves propagating through the fluid, with a very specific frequency. Oscillations of this kind could, for example, lead to variations in the luminosity or in the temperature of the star, and these are quantities that we can measure directly.”In fact, there is already a whole branch of physics called asteroseismology, which studies the internal structure of stars by observing their oscillation modes. This is very much like the way scientists study the internal structure of the Earth by looking at seismic waves. It is possible that the oscillations of a star driven by a dark matter core could also be observed using similar methods. Given the very specific frequencies at which these stars would vibrate, this could be a smoking gun for the presence of dark matter. Asteroseismology is still in its infancy but it will, almost certainly, become a very precise way of observing stars in the future.” © 2015 Phys.org More information: Richard Brito, Vitor Cardoso, and Hirotada Okawa. “Accretion of dark matter by stars.” Physical Review Letters. DOI: 10.1103/PhysRevLett.115.111301, Also at arXiv:1508.04773 [gr-qc] Citation: Dark matter hiding in stars may cause observable oscillations (2015, September 18) retrieved 18 August 2019 from https://phys.org/news/2015-09-dark-stars-oscillations.html Explore further Journal information: Physical Review Letters This document is subject to copyright. Apart from any fair dealing for the purpose of private study or research, no part may be reproduced without the written permission. The content is provided for information purposes only.
What is a Met Office Weather Warning?The Met Office issue weather warnings when there is a risk of weather causing damage, disruption or danger to life. Generally warnings will be issued for heavy rain, wind, ice or snow. They come in three categories. Yellow: The lowest of the three. Yellow means you should plan ahead about potential disruption to travel and other day-to-day activities. These are the most common. Amber: A step up from Yellow, an Amber warning means there is an increased risk of disruption/danger to life and property. Red: These are only issued when ‘extreme weather’ is expected. When one is issued the Met Office advise immediate action is taken to keep yourself and others safe as widespread damage, disruption and risk to life is likely. Red warnings are extremely rare anywhere in the UK and almost unknown in North Staffordshire and South Cheshire. A Cheshire East Council spokesman said: “A yellow weather warning of strong wind is forecast for Cheshire East for tonight and tomorrow. Drive with care & report trees or debris on our roads.” Due to expected ice and snow, Cheshire East Council have also confirmed they will be gritting high level routes in the east of the county, including the A54 and the A537 Cat and Fiddle, from 7.30pm. The spokesman added: “We’ll continue to monitor the weather for further gritting decisions. Please drive with care as windy conditions are expected tonight.” In North Staffordshire Staffordshire County Council have confirmed their gritters will be out in the Staffordshire Moorlands, where snow is already reported this evening – while Stoke-on-Trent City Council say they are monitoring the situation. A County Council spokesman said: “Some freezing temperatures and snow showers expected on higher ground in the Staffordshire Moorlands tonight so gritters will be out. Please take care on the roads.” Read MoreWoman left with serious burns after ‘smoking materials’ set bedding on fire North West Motorway Police, who cover the M6 in Cheshire, are asking motorists to take extra care – particularly on bridges and viaducts. A spokesman said: “Severe weather warning issued overnight and into tomorrow morning for the North West region, not only does this relate to snow but gales of 70-80mph. “High sided vehicles need to take extra care crossing Thelwall Viaduct and Barton Bridge.” A Highways England spokesman added: “Severe weather (snow) is forecast tonight and tomorrow morning for the North East and North West regions. Please check conditions before travelling.” Tips for homeowners in cold weatherThe Met Office has put together a list of handy tips for homeowners in the cold weather: 1. GET YOUR FLU JAB 2. TOP UP YOUR VEHICLE ANTI-FREEZE/SCREEN WASH 3. CHECK YOUR TYRES 4. THINK ABOUT A WINTER KIT FOR YOUR CAR 5. CONSIDER ALTERNATIVE COMMUTING PLANS FOR SEVERE WEATHER 6. CHECK YOUR HEATING – YOUR HOME SHOULD BE HEATED TO AT LEAST 18 °C 7. CONSIDER HOW YOU WOULD ACCESS VITAL INFORMATION IF A STORM TAKES OUT POWER AND PHONELINES 8. CHECK YOUR PIPES ARE INSULATED 9. KNOW WHERE YOUR STOPTAP IS 10. THINK ABOUT WHAT MAY BE IMPACTED BY STRONG WINDS – GUTTERING, PIPES, ROOF TILES/SLATES, GARDEN ITEMS 11. CHECK WHETHER YOU ARE AT RISK OF FLOODING 12. FREEZE A LOAF OF BREAD AND PINT OF MILK FOR TIMES OF BAD WEATHER Elsewhere in the UK an Amber Warning for snow and Yellow warnings for snow and ice are in force across much of the North East and Scotland. The Environment Agency has also issued a number of flood alerts, primarily along coastal areas in Lancashire, East Anglia, the North East and the West Country. Read MoreTeenager arrested following serious assault in city centre Highways England have also announced they may close the A628 route across the Pennines between Derbyshire and South Yorkshire if the weather deteriorates. There are currently no flood warnings or alerts in force in Stoke-on-Trent, Staffordshire or Cheshire. We’ll bring you live updates on the latest traffic and weather news as we get them. Get the biggest Daily stories by emailSubscribeSee our privacy noticeThank you for subscribingSee our privacy noticeCould not subscribe, try again laterInvalid EmailNorth Staffordshire and South Cheshire are set to be battered by strong winds overnight – with power cuts and travel disruption possible, according to the latest forecast from the Met Office. The meteorological agency have updated their Yellow Weather Warning for high winds across the area – with the warning now in force from five minutes past midnight until 9am on Thursday morning. Gusts of up to 70mph are expected as the wind sweeps across Stoke-on-Trent, with the warning saying damage to buildings and flying debris are both a possibility. A Met Office spokesman said: “Strong winds will affect parts of the UK early on Thursday. “The strongest winds are expected to transfer eastwards across the warning area before clearing by mid morning. “Road, rail and ferry services may be affected, with longer journey times and cancellations. There is also a possibility that some bridges may close. “Power cuts may occur, with the potential to affect other services, such as mobile phone coverage. Injuries and danger to life from flying debris are possible, along with some damage to buildings.” Emergency services and bodies responsible for roads are bracing themselves for the wind – with a number of councils announcing plans to grit roads overnight due to the possibility of ice and snow. Read MoreAppeal to trace next-of-kin after death of 66-year-old