The universe teems with weird black holes, gravitational wave hunters find

https://www.sciencemag.org/news/2020/10/universe-teems-weird-black-holes-gravitational-wave-hunters-find?utm_campaign=SciMag&utm_source=JHubbard&utm_medium=Facebook

Less than 5 years ago, physicists rocked the scientific world when they first spotted gravitational waves—fleeting ripples in space and time—set off when two gargantuan black holes billions of light-years away swirled into each other. Since then, scientists have detected a scad of similar events, mostly reported event by event. Today, however, researchers with a global network of gravitational wave detectors announced the first major statistical analyses of their data so far, 50 events in all. Posted online in four papers, the analyses show that black holes—ghostly ultraintense gravitational fields left behind when massive stars collapse—are both more common and stranger than expected. They also shed light on mysteries such as how such black holes pair up before merging.

The new studies, posted on the physics preprint server arXiv, “are superimportant,” says Carl Rodriguez, an astrophysicist at Carnegie Mellon University who was not involved in the work. “With an individual event, there’s only so much you can do in comparing to astrophysics models. But with a catalog you can not only begin to constrain the theory, you can start to understand the landscape.” Selma de Mink, an astrophysicist at Harvard University, says she and her colleagues have been waiting to do their own analyses of the data trove. “There will definitely be a flurry of papers that are rushing to take the first stabs at the data.”

The observations come from three huge L-shaped optical instruments called interferometers that can measure the infinitesimal stretching of space itself by a passing gravitational wave. Two of those detectors belong to the Laser Interferometer Gravitational-Wave Observatory (LIGO), a pair of detectors with arms 4 kilometers long in Louisiana and Washington that spotted the first gravitational waves in 2015. The third detector is Virgo, an interferometer near Pisa, Italy, that has 3-kilometer-long arms and joined the hunt for gravitational waves in 2017.

LIGO and Virgo had already spotted 11 events, including one merger of neutron stars, an event that may shed light on how the universe forges heavy elements. Now, the team has cataloged 37 additional black hole mergers, one likely neutron star merger, and one possible merger of a black hole and neutron star from the first half of its third observing run, from April through September 2019.

Analyses of all 50 events show that when it comes to black holes, “the diversity is surprisingly large,” says Frank Ohme, a gravitational wave astronomer at the Max Planck Institute for Gravitational Physics. From details of the mergers’ chirplike signals, scientists can calculate the masses of the colliding black holes. They expected to find a “mass gap” between about 45 and 135 solar masses—the result of particle physics processes that should blow apart stars within a certain mass range before they can collapse into black holes.

However, LIGO and Virgo have now spotted mergers involving black holes squarely within the gap, including one with a mass of roughly 85 solar masses. De Mink, who models the evolution of black hole pairs from binary star systems, says accounting for the interlopers will be challenging. The mass gap is “such a clear prediction from the models that it’s hard to believe that there’s not a feature there” in the mass spectrum, she says.

Similarly, scientists expected another forbidden range below five solar masses, based on previous observations of individual black holes peacefully orbiting normal stars. But at least one hole in the catalog appears to fall below that limit. “How do you describe the boundaries of this population?” Ohme asks. “It’s not such a clear picture anymore.”.

Their new ability to take a census of black holes has also enabled researchers to probe whether black holes in a merging pair point in the same direction as they orbit each other—a potential clue to how the pair came together in the first place. If the spins align with the orbital axis, the black holes might have formed from a pair of stars that were born together, naturally acquired matching spins, and remained companions after they collapsed. If the spins point in different directions, the black holes might have formed first and then somehow paired later. Which formation channel dominates is a subject of intense debate.

In particular, if one of the black holes spins in the opposite sense of the orbit, the pair would more likely come from the mingling of black holes that had already formed. But it’s very hard to tell for sure whether that’s happening from the warble of a single signal, says Maya Fishbach, an astrophysicist and LIGO member from Northwestern University. However, by analyzing the events en masse, scientists have teased out evidence that at least some of the mergers involve reversed spins. That result in turn suggests that black hole pairs form in more than one way, Fishbach says. “It seems like there might be multiple things going on.”

Rodriguez notes that the overall rate of black hole mergers that LIGO and Virgo see seems to roughly match the rate he predicted in his model, in which already formed black holes find each other and pair in knots of old stars called globular clusters. “I shouldn’t toot my own horn—but I totally am going to,” he says. But, he adds, the data are also consistent with such a mechanism producing just onequarter of the mergers.

Researchers have even been able to probe how the number of black hole mergers may have changed over cosmic time, Fishbach says. The rate is expected to be higher in the early universe, when the pace of star formation was also higher. But previous data allowed that rate to be up to 100,000 times higher than it is now. Now, scientists have seen enough far-flung events to say that the rate of mergers 8 billion years ago was no more than 10 times what it is now, Fishbach says.

LIGO and Virgo scientists owe their scientific bounty to the increasing sensitivity of their detectors, which has enabled them to spot ever fainter and more distant events. Now, they are eager to build up their catalog even further. With more events, they find a correlation between spin alignment and the masses of the black holes that could help reveal whether the heaviest might themselves have formed through mergers. (If the two black holes’ spins aren’t aligned, then they may not have formed from an isolated pair of stars, and theorists wouldn’t necessarily have to explain how a collapsing star could produce such a heavy black hole.) “We’ve answered a lot of questions we didn’t even know we had,” Fishbach says, “but we raised even more. This is just the beginning of the science.”

More, from before.

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93% of Black Lives Matter Protests Have Been Peaceful, New Report Finds

SEPTEMBER 5

https://time.com/5886348/report-peaceful-protests/

The vast majority of Black Lives Matter protests—more than 93%—have been peaceful, according to a new report published Thursday by a nonprofit that researches political violence and protests across the world.

The Armed Conflict Location & Event Data Project (ACLED) analyzed more than 7,750 Black Lives Matter demonstrations in all 50 states and Washington D.C. that took place in the wake of George Floyd’s death between May 26 and August 22.

Their report states that more than 2,400 locations reported peaceful protests, while fewer than 220 reported “violent demonstrations.” The authors define violent demonstrations as including “acts targeting other individuals, property, businesses, other rioting groups or armed actors.” Their definition includes anything from “fighting back against police” to vandalism, property destruction looting, road-blocking using barricades, burning tires or other materials. In cities where protests did turn violent—these demonstrations are “largely confined to specific blocks,” the report says.

The ACLED report includes protests toppling statues of “colonial figures, slave owners and Confederate leaders” as violent incidents. “Since Floyd’s killing, there have been at least 38 incidents in which demonstrators have significantly damaged or torn down memorials around the country,” the report states.

Still, many people continue to believe that Black Lives Matter protests are largely violent—contrary to the report’s findings. ACLED highlights a recent Morning Consult poll in which 42% of respondents believe “most protesters (associated with the BLM movement) are trying to incite violence or destroy property.” ACLED suggests this “disparity stems from political orientation and biased media framing… such as disproportionate coverage of violent demonstrations.”

U.S.-based ACLED is funded by the State Department’s Bureau of Conflict and Stabilization Operations as well as foreign governments and other organizations, including the Dutch Ministry of Foreign Affairs, the German Federal Foreign Office, the Tableau Foundation, the International Organization for Migration, and The University of Texas at Austin. It relied on data collection from the U.S. Crisis Monitor—a joint project led by ACLED and Princeton University’s Bridging Divides Initiative—that tracks and publishes real-time data on political violence and demonstrations in the U.S in order to “establish an evidence base from which to identify risks, hotspots and available resources to empower local communities in times of crisis.”

ACLED also highlights a “violent government response,” in which authorities “use force more often than not” when they are present at protests and that they “disproportionately used force while intervening in demonstrations associated with the BLM movement, relative to other types of demonstrations.” The report also references “dozens of car-ramming attacks” on protesters by various individuals, some of whom have ties to hate groups like the Ku Klux Klan.

ACLED warns in the report that the U.S. “is at heightened risk of political violence and instability going into the 2020 general election,” citing trends in mass shootings, violent hate crimes and police killings. The authors of the report say the Trump administration has exacerbated tensions caused by racial inequality and police brutality. President Donald Trump and high-ranking members of his administration have frequently generalized protesters as violent anarchists.

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Over 90 percent of protests this summer were peaceful, report shows

09/03/20

https://thehill.com/homenews/state-watch/515082-over-90-percent-of-protests-this-summer-were-peaceful-report-shows

Despite several incidents of protests against racism and police brutality turning violent, more than 90 percent of the summer’s protests were peaceful, according to an analysis released Thursday.

The report, produced by the nonprofit Armed Conflict Location and Event Data Project, identified 7,750 protests between May 26 and Aug. 22 in 2,400 locations, according to The Washington Post.

The report found that about 220 became “violent” — a term defined as demonstrators fighting with police or with counterprotesters. The term also applies to demonstrations that resulted in property damage. In 93 percent of cases analyzed, there was no violence.

In the violent cases, the report said, violence was “largely confined to specific blocks, rather than dispersed throughout the city.”

Despite these findings, however, the authors warned that due to the environment of “violent political polarization” in the U.S., violence is likely to occur again if there are issues with the November election.

“In this hyper-polarized environment, state forces are taking a more heavy-handed approach to dissent, non-state actors are becoming more active and assertive, and counter-demonstrators are looking to resolve their political disputes in the street,” the authors wrote, according to the Post.

“Without significant mitigation efforts, these risks will continue to intensify in the lead-up to the vote, threatening to boil over in November if election results are delayed, inconclusive, or rejected as fraudulent,” they added.

Demonstrations erupted nationwide over police brutality and racial injustice after the killing of George Floyd, an unarmed Black man who died in Minneapolis Police custody in late May.

Protesters, advocates and lawmakers took to the streets in cities and towns all over the U.S. to demand police reform at the state and federal levels.

In late August, another Black American, Jacob Blake, was shot in the back seven times while trying to enter his vehicle in Kenosha, Wis. The man is currently paralyzed from the waist down.

Blake’s shooting once again sparked protests in Wisconsin and has led to violent clashes between protesters and counterprotesters. On the third night of demonstrations in Kenosha, two protesters were shot and killed and one was injured.

The report also suggested disproportionate police response had escalated tensions at protests. In about 10 percent of Black Lives Matter protests, law enforcement intervened, using force such as batons, rubber bullets or pepper spray in about half those cases.

“The heavy-handed police response appears to have inflamed tensions and increased the risk of violent escalation,” the report states, according to the Post.

“The escalating use of force against demonstrators comes amid a wider push to militarize the government’s response to domestic unrest, and particularly demonstrations perceived to be linked to left-wing groups like antifa, which the administration views as a ‘terrorist’ organization,” it added.

The Trump administration has come under fire after law enforcement deployed tear gas on protesters in Lafayette Square in Washington, D.C., earlier in the summer.

The report specifically cites the deployment of federal officers to Portland, Ore., as escalating already intense protests. Fewer than a quarter of Portland protests were met with force in May or June, compared to 40 percent in July and August. The number of violent demonstrations increased about 10 points, from 53 percent to 63 percent.

Reports surfaced in recent months that unmarked federal agents were grabbing protesters in Portland, Ore., and holding them in unmarked vehicles, sparking outrage from local lawmakers.