Tag Archives: tidal

Britain resurfaces huge tidal energy plan amid Ukraine crisis

An aerial shot of the Severn Estuary from 2010.

Jamie Cooper | Sspl | Getty Images

An independent commission in the U.K. is to revisit the possibility of using the Severn Estuary, a large body of water between England and Wales, to harness tidal energy.

The commission will be set up by the pan-regional Western Gateway Partnership, which covers western England and south Wales.

“The time is right to look again at what could be an incredible source of clean, environmentally friendly energy on our doorstep,” Jane Mudd, who is vice chair of the partnership and also leads Newport City Council, said in a statement Tuesday.

The commission, Mudd added, would “have the expertise and independence it needs to explore whether using the Severn Estuary to create sustainable power is attainable and viable.”

Katherine Bennett, the Western Gateway Partnership’s chair, said it had been known for some time that the Severn had “huge potential for creating clean renewable energy.”

According to a paper published by the Institution of Civil Engineers in 2016, the output from the Severn’s tidal range could be approximately 25 terawatt hours per year, or “about 7% of the UK energy needs.”

While there is excitement about tidal power’s prospects, the newest proposal is in its very early stages and any project would require significant levels of investment.

“No decisions have been made about what a potential solution for getting power from the Severn might look like or whether any development will take place,” the Western Gateway Partnership said.

The notion of harnessing the Severn Estuary’s tides to generate power has been mooted for many years. This is because the tidal range — a term which refers to the height difference between low and high tide — is one of the world’s largest, at up to 14 meters.

Despite this huge resource, projects have never gotten off the ground. Back in 2010, the U.K. government said it did not “see a strategic case to bring forward a Severn tidal power scheme in the immediate term.”

“The costs and risks for the taxpayer and energy consumer would be excessive compared to other low-carbon energy options,” the government added.

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The establishment of the new commission comes at a time when concerns about Europe’s reliance on Russian oil and gas have been brought into sharp focus following the invasion of Ukraine last month.

Huw Thomas, a Western Gateway board member, acknowledged previous tidal power schemes had not garnered support from the U.K. government “due to a perceived requirement for high levels of public investment and concerns over the environmental impact on designated areas in the Severn Estuary.”

“However, the changing landscape of the climate emergency, energy insecurity, rising costs, and rapid technological improvements indicate that many of these policy, cost and environmental barriers may no longer be as significant,” Thomas, who is also the leader of Cardiff City Council, said.

In comments published by the Guardian on Tuesday, Michael Gove, the U.K.’s secretary of state for levelling up, housing and communities, offered his support for the commission.

“Russia’s invasion has served to heighten concerns about energy security and costs,” the Guardian reported Gove as saying.

“Sustainable forms of energy cannot come soon enough. The launch of an independent commission on tidal energy for the Severn is very welcome news.”

Tidal power has been around for decades — EDF’s 240 MW La Rance tidal power plant in France dates back to the 1960s — but recent years have seen a number of new projects take shape.

In July 2021, a tidal turbine weighing 680 metric tons started grid-connected power generation at the European Marine Energy Centre in Orkney, an archipelago located north of mainland Scotland.

And in October, plans for a £1.7 billion (around $2.24 billion) project in the U.K. incorporating technologies including underwater turbines were announced.

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How to Export Your Entire Spotify Library for Free

Photo: nikkimeel (Shutterstock)

There are many reasons to move away from Spotify. Apple Music now has lossless audio at a cheaper rate. If you use Amazon Prime, Prime Music comes free; if you have an Echo smart speaker, it’s the cheapest way to stream your music. Spotify doesn’t have music by Neil Young or Joni Mitchell. No matter the reason, there’s never been more competition between music streaming services.

Sadly, streaming services aren’t exactly eager to make it easy for you to export your library so you can take it with you—but there are many third-party websites, apps, and services that can fill that gap.

Use SongShift to switch from Spotify to Apple Music

Screenshot: Khamosh Pathak

If you use an iPhone or an iPad and are moving from Spotify to Apple Music, use the SongShift app. The app has been a go-to solution for the past couple of years, and it’s still the best. More importantly, it’s fast and it’s free.

Well, sort of. While SongShift puts a limit of 100 songs per playlist transfer, its Library Transfer feature is free. So if you’re OK moving all your music to Apple Music and then recreating your longest playlists, you can get away with using the free tier. SongShift supports Spotify, Apple Music, Amazon Prime Music, Tidal, YouTube Music, Deezer, and Pandora, and you can even export in JSON or text files. If you’ve spent a lot of time creating playlists, it might be worth paying for the $4.99/month subscription, moving all your playlists, and then canceling it.

To get started, open the SongShift app, and connect both Spotify and Apple Music accounts to the app. Then, tap the Plus button from the top. Tap “Setup Source,” choose “Spotify” from the “Songs” tab, and from the selection page, go with the “Full Library Transfer” option.

Next, tap “Setup Destination” from the “User Library” tab, and go with Apple Music. Tap “Continue,” and select “I’m Finished.” Now, let SongShift do its thing.

After the process is done, you’ll find your music in Apple Music, or any other music streaming service.

Use TuneMyMusic on the web

Screenshot: Khamosh Pathak

If you don’t use an iPhone, or if you want to use a web-based service that works on any platform, go with TuneMyMusic. It lets you transfer playlists and your entire library between Spotify, Apple Music, YouTube, YouTube Music, Deezer, Tidal, Amazon Prime Music, Pandora, and more. You can transfer 500 songs for free. To transfer more songs, you’ll need to use the $4.50/month premium plan.

Open the TuneMyMusic website and click the big “Let’s Begin” button. Then, choose “Spotify” from the source list, connect your account, and click the “Load from your Spotify Account” button. Here, you can choose different playlists, or you can use the “Favorite Songs” option to transfer your Liked Songs (your entire library).

Then, go to the next page, and choose your destination service. Connect the service and click the “Start Moving My Music” button to start the process.

Use FreeYourMusic for free song transfer on any platform

If you don’t like the TuneMyMusic service, and you don’t mind using an app, try out the FreeYourMusic service. It’s available for Android, iPhone, Windows, and Mac. It offers unlimited song transfers for free.

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‘Tidal wave’: Omicron could put U.S. COVID-19 surge into overdrive

Dec 17 (Reuters) – Two years into the coronavirus pandemic, the United States is confronting another dark winter, with the red-hot Omicron variant threatening to worsen an already dangerous surge of cases.

Hospitalizations for COVID-19 have jumped 45% over the last month, and cases have increased 40% to a seven-day average of 123,000 new infections a day, according to a Reuters tally.

Pfizer Inc (PFE.N), one of the chief vaccine makers, on Friday predicted the pandemic would last until 2024 and said a lower-dose version of its vaccine for children ages 2 to 4 generated a weaker-than-expected immune response, which could delay authorization. read more

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The National Football League rescheduled three weekend games after multiple teams were hard hit by outbreaks. read more

The National Hockey League added another game to its recent list of postponements, raising fresh concerns about the league’s plan to send the world’s top players to the Beijing Olympics in February. read more

In New York City, Radio City Music Hall announced that Friday’s four performances of the Rockettes’ iconic Christmas show were canceled due to breakthrough cases. The Michael Jackson musical “MJ” on Broadway canceled performances through Dec. 27, joining other Broadway productions that have called off shows after cast and crew members tested positive.

The Omicron variant appears to be far more transmissible than previous iterations and more agile in evading immune defenses, according to early studies.

Public health officials say it is likely to become the dominant variant in the country, following fast-moving spreads in countries such as South Africa and the United Kingdom, and could strain hospitals still struggling to contain this summer’s Delta variant surge.

“GET BOOSTED NOW. Tidal wave of Omicron likely coming to a hospital near you soon,” Dr. Tom Frieden, former chief of the Centers for Disease Control and Prevention (CDC), posted on Twitter.

Preliminary data in South Africa suggests Omicron leads to milder illness than the Delta variant, which is still driving much of the current wave. But a British study released on Friday found no difference in severity between the two variants. read more

Either way, Omicron’s extraordinary level of infectiousness means it could cause many additional deaths, the top U.S. infectious disease expert, Dr. Anthony Fauci, said on Friday.

“When you have a larger number of people getting infected, the total amount of hospitalizations is going to be more. That’s just simple math,” Fauci told CNBC.

Fauci also said officials are discussing whether to redefine what it means to be “fully vaccinated” to include booster shots.

PULLING THE PLUG?

The latest surge is creating yet another round of disruptions to daily life, though widespread lockdowns have not been put in place.

Some Americans have reconsidered holiday plans. Winifred Donoghue, a New York City advertising writer, canceled a Jan. 8 disco party at her family’s vacation home in Highland Lakes, New Jersey, that was intended to be a joint celebration of her 60th birthday and the new year.

“Two weeks ago, everyone was boosted. Then the infections went up exponentially,” she said. “By January, who is going to feel safe? I just pulled the plug on it.”

Eric Hrubant, the chief executive of CIRE Travel, said he hadn’t yet seen a wave of cancellations, as he did in August when the Delta variant swept the country. But worried clients have inundated the agency with calls about new COVID-19 protocols, such as mandatory travel quarantines.

“People aren’t panicking,” he said. “People are making educated decisions.”

Several states have hit alarming levels of cases and hospitalizations. The U.S. states reporting the highest seven-day average of infections were New York, Ohio, Pennsylvania, Illinois and Michigan, according to a Reuters tally.

In Ohio, exhausted hospital workers will be getting some help starting on Monday from 1,050 National Guard troops – including 150 nurses, emergency medical technicians and others with medical training, Governor Mike DeWine said on Friday.

The CDC released a new “test-to-stay” strategy on Friday that allows unvaccinated children to remain in school even if they are exposed to the virus. read more

The protocol is intended to replace automatic quarantines, which have required tens of thousands of students to miss school days this fall.

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Reporting by Joseph Ax in Princeton, New Jersey, and Barbara Goldberg in Maplewood, New Jersey; Additional reporting by Nandita Bose, Carl O’Donnell, Roshan Abraham, Jill Serjeant, Susan Heavey, Caroline Humer, Mrinalika Roy, Leroy Leo and Frank Pingue; Editing by Howard Goller and Cynthia Osterman

Our Standards: The Thomson Reuters Trust Principles.

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UK battles Omicron ‘tidal wave’ with booster jabs as infections rise and first death from variant recorded

On Monday, UK Prime Minister Boris Johnson confirmed the country’s first death of a person with the variant. He told reporters at a vaccination clinic: “I think the idea that this is somehow a milder version of the virus, I think that’s something we need to set on one side and just recognize the sheer pace at which it accelerates through the population.”

The United Kingdom increased its Covid-19 alert level on Sunday and is once again accelerating its rollout of booster jabs in an effort to respond to the new wave of cases.

Health Secretary Sajid Javid warned on Monday that the data on Omicron infections is unlike that of earlier variants.

“It’s spreading at a phenomenal rate, something that we’ve never seen before — it’s doubling every two to three days in infections,” Javid told Sky News on Monday. He added that it was too soon to tell if cases of the new variant are milder.

“That means we’re facing a tidal wave of infection, we’re once again in a race between the vaccine and the virus,” he added, echoing language used by Johnson in a televised address on Sunday night.

On Sunday, the Prime Minister set a new target of offering all adults a third shot by the end of December — a month earlier than originally planned. He had previously cut the interval between second and third doses from six months to three. The British government has focused its Covid response around the vaccine program since last summer, and had resisted reimposing restrictions until the Omicron variant came to light.

“I’m afraid it is now clear that two doses of vaccine are simply not enough to give the level of protection we all need,” Johnson said, citing early data that showed the effectiveness of a two-dose regimen is diminished by the new variant, but that boosters still provide a good level of protection.

“No-one should be in any doubt: There is a tidal wave of Omicron coming,” Johnson said. “But the good news is that our scientists are confident that with a third dose — a booster dose — we can all bring our level of protection back up.”

The UK has so far reported 3,137 cases of the Omicron variant, though the true number is likely to be higher. Javid said “about 10 people” are in hospital with the new variant. Overall, the country’s seven-day rolling average of Covid-19 cases has surpassed 50,000 a day.

Omicron was probably behind around 40% of infections in London, Javid said on Monday. But Johnson said that “tomorrow it’ll be the majority of the cases,” underlining how rapid the spread of the new strain has been in its first weeks in Britain.

New guidelines asking people to work from home came into force on Monday. The UK has also brought back its mask mandate for shops and public transport, and now requires proof of vaccination or a negative test for attendees of large events.

The recent flurry of new restrictions marks a sharp turn from the past few months, during which Johnson resisted Europe’s turn towards long-term mitigation measures like vaccine passports and mask mandates.

But the embattled Prime Minister has faced a significant rebellion from his own Conservative backbenchers over his move to reintroduce Covid rules, relying on support from the opposition Labour Party to pass them into law.

Johnson is also embroiled in a scandal over reports that Downing Street held a number of staff parties last winter when the rest of the UK was living under strict rules banning social mixing. He has been forced to deny he fast-tracked Covid rules in order to distract from his political woes.

CNN’s Robert Iddiols contributed reporting.

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Jaw-Dropping Simulation Shows Stars Shredded as They Get Too Close to a Black Hole

We just got a little more insight into stellar death by black hole.

In a series of simulations, a team of astrophysicists has chucked a bunch of stars at a range of black holes, and recorded what happens.

 

It’s the first study of its kind, the scientists said, that combines Einstein’s theory of general relativity with realistic models of the densities of main-sequence stars. The results will help us understand what is happening when we observe the flares of light from distant black holes shredding unfortunate stars.

And the simulations, supporting a paper that was published last year, are also gorgeous as heck.

When a star ventures a little too close to a black hole, things turn violent pretty quickly. The extreme gravitational field of the black hole starts deforming and then pulling the star apart, due to what we call tidal forces – the stretching of one body due to the gravitational pull of another.

When a star gets so close to a black hole that the tidal force results in material being stripped from the star, we call that a tidal disruption event.

In the worst-case scenario for the star, there’s no escape. The disruption is total, and some of the star’s material gets slurped down onto the black hole like a spaghetti noodle.

But not every encounter between a black hole and a star ends this way. Some stars have been observed surviving. The simulations, led by astrophysicist Taeho Ryu of the Max Planck Institute for Astrophysics in Germany, were designed to find out what factors contributed to a star’s survival.

 

The team created six virtual black holes, with masses between 100,000 and 50 million times that of the Sun. Each of these black holes then had encounters with eight main-sequence stars, with masses between 0.15 and 10 times that of the Sun.

They found that the main factor that contributed to a star’s survival was the initial density of the star. The denser the star, the more likely it is to survive an encounter with a black hole. In the video above, you can see these encounters play out around a supermassive black hole 1 million times the Sun’s mass. The stars with the highest density are yellow, and the lowest are blue.

The team also found that partial disruptions occur at the same rate as total disruptions, and the proportion of the star’s mass that is lost can be described surprisingly easily using a simple expression.

Future research to fill in the finer details will help model the effects of these encounters, including the heretofore relatively neglected partial disruption events, the researchers said.

This will reveal what can happen to a star after it survives an encounter with a black hole; whether it continues along the main sequence, or turns into a stellar remnant; and if it will continue in orbit around the black hole to meet total disruption at a later date.

The paper accompanying the simulations was published in The Astrophysical Journal in 2020.

 

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DC-Baltimore region braces for tidal flooding that could be the worst in two decades

“One of the biggest tidal flood events of the past 10-20 years (possibly since Hurricane Isabel at some locales), is expected Friday & Saturday. Those along tidal shores should get ready for exceptional tidal inundation!” the local National Weather Service (NWS) said in a tweet.

With two to four feet of coastal flooding expected, more than 20 million people are under alerts, including residents of Baltimore and Washington. Parts of northern Virginia are also under a flood watch through Friday afternoon, NWS said.

To help Baltimore residents prepare for the potentially historic storm, the city’s Department of Transportation will distribute sandbags to residents from 9 a.m. to 3 p.m. Friday on a first-come, first-served basis, CNN affiliate WJZ reported.

The last time conditions were this bad was during Hurricane Isabel in 2003.

During that storm, Fell’s Point in Baltimore, the US Naval Academy, downtown Annapolis, and the Belle View neighborhoods of northern Fairfax County, Virginia, all experienced severe storm surge flooding, according to the National Oceanic and Atmospheric Administration.

Businesses already preparing for flooding

By 1 a.m. Friday, the Potomac River in Washington, DC, experienced minor flooding, which was expected to get worse into Saturday before subsiding, according to the NWS. The Severn River in Annapolis, Maryland, will also see similar conditions.

And high wind warnings and wind advisories are also in effect for several counties as wind gusts are expected to reach as high as 60 miles per hour.

“Damaging winds will blow down trees and power lines. Widespread power outages are expected. Travel will be difficult, especially for high profile vehicles,” the local NWS said.

Businesses were bracing for the impact by placing sandbags to protect their premises.

In Alexandria, Stu Robinson, the general manager at Misha’s Coffee, removed all outdoor furniture and started loading sandbags, CNN affiliate WTTG reported.
Konrad Karandy, who manages Mission BBQ in Annapolis, told CNN affiliate WJZ that he’s doing everything he can to keep the water away from his business, including piling sandbags.

“We’re prepping for the worst. My personal guess is four feet (of water), something like that,” Karandy told the news outlet.

Sharon Mahaffey who works with Storm Bros. Ice Cream in Annapolis added: “We’ve already gotten sandbags out. We’re moving supplies that could potentially get wet.”

D.C. Homeland Security and Emergency Management Director Christopher Rodriguez told the outlet that businesses along the coast will likely need their flood insurance documents ready.

“We want to make sure that our businesses that are along those coastal areas of our region, in particular our city, make sure you know where your insurance papers are, because flood insurance is going to be really helpful as we recover from this event over the next 48 hours,” Rodriguez said.

And in Maryland, schools in Calvert and Harford counties announced Thursday night they will close due to the potential flooding, according to the the affiliate.

CNN’s Allison Chinchar contributed to this report.



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Weather news: “One of the biggest tidal flood events of the past 10-20 years,” say forecasters

“Right now we’re expecting it to be one of the worst tidal flooding events that we’ve had in the past 10 or 20 years for a lot of locations in the Chesapeake Bay watershed,” Chris Strong, the warning coordination meteorologist at the National Weather Service (NWS) in Sterling, Virginia, tells CNN Weather. “The biggest impact that we’re expecting here in the Baltimore/Washington area and along the Chesapeake Bay is the tidal flooding.”

Flooding is expected to peak on Friday and linger through Saturday. During this time, two to four feet of coastal flooding is likely.

The last time conditions were this bad was during Hurricane Isabel in 2003.

During that storm, Fell’s Point in Baltimore, the U.S. Naval Academy, downtown Annapolis, and the Belle View neighborhoods of northern Fairfax County, Virginia, all experienced severe storm surge flooding, according to the NOAA.

While Strong warns that the flooding with Isabel was several feet higher than what is forecast for this storm, this will be one of the worst tidal flooding events since that hurricane in 2003.

The river gauge for Chesapeake Bay at Cambridge, Maryland, is forecast to reach over 5 feet. This would make it the second highest tide on record, behind a height of 6.2 feet which was reached back in 2003 during Hurricane Isabel.
Another worrisome location is the St George Creek at Straits Point river gauge where the current forecast calls for a maximum height of 5.2 feet, putting it over the threshold for major flooding. If it reaches that high it would break the previous all-time record of 4.56 feet set in 2018.
At just 3.5 feet, water historically “covers roads on St. Georges Island, is in yards, and approaching structures,” according to the National Weather service.
“Water anomalies are already up to 2 ft at Straits Point and rising, and Annapolis has been hovering around minor flood stage even as the astro tide is going into low tide,” the NWS in Baltimore said.

As of Thursday afternoon, the forecast crest for Annapolis City Dock is 5.1 feet. If the water level does hit 5 feet, there will be significant and widespread flooding along the lower Tidal Potomac and adjacent tidal tributaries. Numerous roads and structures would also be affected.

“At that water level, the historic Annapolis City Dock will be flooded and will look like St. Marks Square in Venice when it floods,” says Chad Myers, CNN Meteorologist.
But even when the tide reaches just 4.2 feet, the boardwalk at the Annapolis City Dock is underwater. Water also affects several locations near the city dock, including portions of Compromise Street and several streets on the Naval Academy campus.
If the water reaches 6 feet, there will be significant flooding in the Annapolis City Dock area, and on portions of the Naval Academy campus. Numerous roads and fields typically flood at that height, and water seeps into several buildings.

“Usually, when we have tidal events this extreme, it’s usually from hurricanes or tropical events,” Strong said. “This is just low pressure moving in, but that strong low pressure is working against high pressure over New England to our north. That combination is driving the easterly flow right off the Atlantic Ocean and piling all that Atlantic ocean water on the shoreline and up the Chesapeake Bay.”

High wind warnings and wind advisories are also in effect for several counties as wind gusts are expected to reach as high as 60 mph.

“Damaging winds will blow down trees and power lines,” the warning says. “Widespread power outages are expected. Travel will be difficult, especially for high profile vehicles.”

It is important to note that for the Chesapeake Bay at Cambridge location, four of the five highest crests on record have occurred since September of 2003.

Chesapeake Bay at Windmill Point has registered 8 out of their 10 highest crests on record since September of 2006.

“Long-term sea level rise from rising global and ocean temperatures resulting from climate change makes coastal flooding events like this happen more frequently, with worsening impacts from higher floods,” says Brandon Miller, CNN meteorologist and climate crisis beat leader. “Sea levels have risen nearly a foot since the beginning of the 1900’s, which raises the baseline from which these floods occur — pushing nuisance floods from storms into record territories that used to only come in the strongest storms such as hurricanes.”

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‘World’s most powerful tidal turbine’ starts to export power to grid 

A tidal turbine weighing 680 metric tons and dubbed “the world’s most powerful” has started grid-connected power generation at the European Marine Energy Centre in Orkney, an archipelago located north of mainland Scotland.

The news marks another major step forward for the U.K.’s nascent marine energy sector. 

In an announcement Wednesday, Scottish engineering firm Orbital Marine Power explained how its 2 megawatt O2 turbine had been anchored in a body of water called the Fall of Warness, with a subsea cable linking it to a local electricity network on land. 

It’s expected that the turbine, which is 74-meters long, will “operate in the waters off Orkney for the next 15 years” and have “the capacity to meet the annual electricity demand of around 2,000 UK homes.”

The turbine is also set to send power to a land-based electrolyzer that will generate so-called green hydrogen. In a statement, Orbital Marine Power’s CEO Andrew Scott described Wednesday’s news as “a major milestone for the O2.”

Funding for the O2’s construction has come from public lenders via Abundance Investment. The Scottish government has also provided £3.4 million (around $4.72 million) of support through its Saltire Tidal Energy Challenge Fund.

Michael Matheson, the Scottish government’s cabinet secretary for net zero, energy and transport said his country was “ideally-placed to harness the enormous global market for marine energy.”

“The deployment of Orbital Marine Power’s O2, the world’s most powerful tidal turbine, is a proud moment for Scotland and a significant milestone in our journey to net zero,” he went on to add.

Looking to the future, Orbital Marine Power said it was “setting its sights” on the commercialization of its tech via the deployment of multi-megawatt arrays.

With miles of coastline, the U.K. as a whole is home to a number of projects related to marine energy.

In April, it was announced that a year-long research project focusing on the potential of tidal, wave and floating wind technology had secured support from Marine-i, a program centered around innovation in areas such as marine energy.

The project will be based on the Isles of Scilly, an archipelago located off the southwest coast of England, and led by Isles of Scilly Community Venture, Planet A Energy and Waves4Power.

There’s also potential when it comes to rivers. Back in March, the Port of London Authority gave the go ahead for trials of tidal energy technology on a section of the River Thames, a move which could eventually help to decarbonize operations connected to the river.

While interest in marine-based energy systems appears to be growing, the current footprint of the industry and its technologies remains small.

Figures from Ocean Energy Europe show that only 260 kilowatts (kW) of tidal stream capacity was added in Europe last year, while just 200 kW of wave energy was installed.

By contrast, 2020 saw 14.7 gigawatts of wind energy capacity installed in Europe, according to industry body WindEurope.

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An Entire Swarm of Black Holes Has Been Caught Moving Through The Milky Way

A fluffy cluster of stars spilling across the sky may have a secret hidden in its heart: a swarm of over 100 stellar-mass black holes.

If this finding can be validated, it will explain how the cluster came to be the way it is – with its stars spaced light-years apart, smearing out into a stellar stream stretching across 30,000 light-years.

 

The star cluster in question is called Palomar 5, located around 80,000 light-years away. Such globular clusters are often considered ‘fossils’ of the early Universe. They’re very dense and spherical, typically containing roughly 100,000 to 1 million very old stars; some, like NGC 6397, are nearly as old as the Universe itself.

In any globular cluster, all its stars formed at the same time, from the same cloud of gas. The Milky Way has around 150 known globular clusters; these objects are excellent tools for studying, for example, the history of the Universe, or the dark matter content of the galaxies they orbit.

But there’s another type of star group that is gaining more attention – tidal streams, long rivers of stars that stretch across the sky. Previously, these had been difficult to identify, but with the Gaia space observatory working to map the Milky Way with high precision in three dimensions, more of these streams have been brought to light.

“We do not know how these streams form, but one idea is that they are disrupted star clusters,” explained astrophysicist Mark Gieles of the University of Barcelona in Spain.

 

“However, none of the recently discovered streams have a star cluster associated with them, hence we can not be sure. So, to understand how these streams formed, we need to study one with a stellar system associated with it. Palomar 5 is the only case, making it a Rosetta Stone for understanding stream formation and that is why we studied it in detail.”

Palomar 5 appears unique in that it has both a very wide, loose distribution of stars and a long tidal stream, spanning more than 20 degrees of the sky, so Gieles and his team homed in on it.

The team used detailed N-body simulations to recreate the orbits and evolutions of each star in the cluster, to see how they could have ended up where they are today.

Since recent evidence suggests that populations of black holes could exist in the central regions of globular clusters, and since gravitational interactions with black holes are known to send stars careening away, the scientists included black holes in some of their simulations.

Their results showed that a population of stellar-mass black holes within Palomar 5 could have resulted in the configuration we see today. Orbital interactions would have slingshot the stars out of the cluster and into the tidal stream, but only with a significantly higher number of black holes than predicted.

 

The stars escaping the cluster more efficiently and readily than black holes would have altered the proportion of black holes, bumping it up quite a bit.

“The number of black holes is roughly three times larger than expected from the number of stars in the cluster, and it means that more than 20 percent of the total cluster mass is made up of black holes,” Gieles said.

“They each have a mass of about 20 times the mass of the Sun, and they formed in supernova explosions at the end of the lives of massive stars, when the cluster was still very young.”

In around a billion years, the team’s simulations showed, the cluster will dissolve completely. Just before this happens, what remains of the cluster will consist entirely of black holes, orbiting the galactic center. This suggests that Palomar 5 is not unique, after all – it will dissolve completely into a stellar stream, just like others that we have discovered.

It also suggests that other globular clusters will likely share the same fate, eventually. And it offers confirmation that globular clusters may be excellent places to look for black holes that will eventually collide, as well as the elusive class of middleweight black holes, between stellar mass lightweights and supermassive heavyweights.

“It is believed that a large fraction of binary black hole mergers form in star clusters,” said astrophysicist Fabio Antonini of Cardiff University in the UK.

“A big unknown in this scenario is how many black holes there are in clusters, which is hard to constrain observationally because we can not see black holes. Our method gives us a way to learn how many black holes there are in a star cluster by looking at the stars they eject.”

The research has been published in Nature Astronomy.

 

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Something Invisible Is Tearing Apart The Nearest Star Cluster to Earth

Strange things are afoot in the Milky Way.

According to a new analysis of Gaia satellite data, the closest star cluster to our Solar System is currently being torn apart – disrupted not just by normal processes, but also by the gravitational pull of something massive we can’t see.

 

This disruption, astronomers say, could be a hint that an invisible clump of dark matter is nearby, wreaking gravitational havoc on anything within its reach.

Actually, star clusters being pulled apart by gravitational forces is inevitable. A star cluster is, as the name suggests, a tight, dense concentration of stars. Even internally, the gravitational interactions can get pretty rowdy.

Between those internal interactions and external galactic tidal forces – the gravity exerted by the galaxy itself – star clusters can end up pulled apart into rivers of stars: what is known as a tidal stream.

These streams are hard to see in the sky, because it’s often quite tricky to gauge stellar distances, and therefore group stars together. But the Gaia satellite has been working to map the Milky Way galaxy in three dimensions with the most detail and highest precision achievable, and the most accurate position and velocity data on as many stars as possible.

Because stars pulled from a star cluster still share the same velocity (more or less) as the stars in the cluster, the Gaia data has helped astronomers identify many previously unknown tidal streams, and star clusters with tidal tails – threads of stars that have started to come loose from the cluster both in front and behind it.

 

In 2019, astronomers revealed they had found evidence in the second Gaia data release of tidal tails streaming from the Hyades; at 153 light-years away, it’s the closest star cluster to Earth.

This caught the attention of astronomer Tereza Jerabkova and her colleagues from the European Space Agency and the European Southern Observatory. When Gaia Data Release 2.5 (DR2.5) and DR3 became available, they homed in, expanding the search parameters to catch the stars the earlier detections had missed.

They found hundreds and hundreds of stars associated with the Hyades. The central cluster is about 60 light-years across; the tidal tails span thousands of light-years.

Having such tails is fairly normal for a star cluster disrupted by galactic tidal forces, but the team noticed something weird. They ran simulations of the cluster’s disruption, and found significantly more stars in the trailing tail of the simulation. In the real cluster, some stars are missing.

The team ran more simulations to find out what could cause these stars to go astray – and found that an interaction with something big, about 10 million times the mass of the Sun, could reproduce the observed phenomenon.

 

“There must have been a close interaction with this really massive clump, and the Hyades just got smashed,” Jerabkova said.

The big problem with that scenario is that we can’t currently see anything that massive anywhere nearby. However, the Universe is actually full of invisible stuff – dark matter, the name we give to the mysterious mass whose existence we can only infer by its gravitational effects on the things we can see.

According to these gravitational effects, scientists have calculated that roughly 80 percent of all matter in the Universe is dark matter. It’s thought that dark matter is an essential part of galaxy formation – large clumps of it in the early Universe collected and shaped the normal matter into the galaxies we see today.

Schematic diagram of our galaxy’s dark matter halo. (Digital Universe/American Museum of Natural History)

Those dark matter clumps can still be found today in extended ‘dark halos’ around galaxies. The Milky Way has one thought to be 1.9 million light-years across. Within those halos, astronomers predict denser clumps, called dark matter subhalos, just drifting around.

Future searches may turn up a structure that could have caused the weird disappearance of stars in the trailing tail of Hyades; if they don’t, the researchers think the disruption could be the work of a dark matter subhalo.

The finding also suggests that tidal streams and tidal tails could be excellent places to look for sources of mysterious gravitational interactions.

“With Gaia, the way we see the Milky Way has completely changed,” Jerabkova said. “And with these discoveries, we will be able to map the Milky Way’s sub-structures much better than ever before.”

The research has been published in Astronomy & Astrophysics.

 

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