[youtube https://www.youtube.com/watch?v=uzF3eFN-WdE&w=800&h=450]
Scientists using the Hubble Space Telescope have found evidence for an intermediate-mass black hole in the closest globular cluster to Earth, Messier 4.

NASA published this original story on May 23, 2023. Edits by EarthSky.

The 3 types of black holes

Astronomers using NASA’s Hubble space telescope have powerful evidence for the presence of a rare class of intermediate-mass black holes that might be lurking in the heart of the closest globular star cluster to Earth – Messier 4 – located somewhere between 6,000 to 7,200 light-years away.

Black holes are like intense gravitational potholes in the fabric of space, and they all seem to come in two sizes: small and humongous. Scientists estimate that 100 million small black holes litter our galaxy. These small black holes, created from exploded stars, are several times the mass of our sun. Meanwhile, supermassive black holes flood the universe at large. These behemoths weigh millions or billions of times our sun’s mass and lie at the centers of galaxies.

But scientists have long-sought a missing link: the intermediate-mass black hole. These black holes would weigh somewhere between 100 and 100,000 solar masses. How would they form, where would they hang out, and why do they seem so rare?

Hunting for an intermediate-mass black hole

Astronomers have identified other possible intermediate-mass black holes through a variety of observational techniques. Two of the best candidates — 3XMM J215022.4-055108, which Hubble helped discover in 2020, and HLX-1, identified in 2009 — reside in dense star clusters in the outskirts of other galaxies. Each of these possible black holes has the mass of tens of thousands of suns. And, they may have once been at the centers of dwarf galaxies. NASA’s Chandra X-ray observatory has also helped make many possible intermediate black hole discoveries, including a large sample in 2018.

Looking much closer to home, scientists have detected many suspected intermediate-mass black holes in dense globular star clusters orbiting our Milky Way galaxy. For example, in 2008, Hubble astronomers announced the suspected presence of an intermediate-mass black hole in the globular cluster Omega Centauri. For many reasons, including the need for more data, these and other intermediate-mass black hole findings still remain inconclusive and do not rule out alternative theories.

Targeting M4

Scientists have now used Hubble to zero in on the core of the globular star cluster Messier 4 (M4). They’re black-hole hunting with higher precision than was possible in previous searches. Eduardo Vitral of the Space Telescope Science Institute in Baltimore, Maryland, is the lead author on a paper to be published in the Monthly Notices of the Royal Astronomical Society.

Vitral’s team has detected a possible intermediate-mass black hole of roughly 800 solar masses. The suspected object isn’t visible. However, the team can calculate its mass by studying the motion of stars caught in its gravitational field, like bees swarming around a hive. Measuring their motion takes time and a lot of precision. This is where Hubble accomplishes what no other present-day telescope can do. Astronomers looked at 12 years’ worth of M4 observations from Hubble and resolved pinpoint stars.

His team estimates that the black hole in M4 could be as much as 800 times our sun’s mass. Hubble’s data tend to rule out alternative theories for this object. Some of those theories would be a compact central cluster of unresolved stellar remnants like neutron stars, or smaller black holes swirling around each other. Vitral said:

We have good confidence that we have a very tiny region with a lot of concentrated mass. It’s about three times smaller than the densest dark mass that we had found before in other globular clusters. The region is more compact than what we can reproduce with numerical simulations when we take into account a collection of black holes, neutron stars, and white dwarfs segregated at the cluster’s center. They are not able to form such a compact concentration of mass.

Eliminating alternatives to the intermediate-mass black hole

A grouping of close-knit objects would be dynamically unstable. If the object isn’t a single intermediate-mass black hole, it would require an estimated 40 smaller black holes crammed into a space only 1/10 of a light-year across to produce the observed stellar motions. The consequences are that they would merge and/or be ejected in a game of interstellar pinball. Vitral explained their process:

We measure the motions of stars and their positions, and we apply physical models that try to reproduce these motions. We end up with a measurement of a dark mass extension in the cluster’s center. The closer to the central mass, more randomly the stars are moving. And, the greater the central mass, the faster these stellar velocities.

Because intermediate-mass black holes in globular clusters have been so elusive, Vitral cautions:

While we cannot completely affirm that it is a central point of gravity, we can show that it is very small. It’s too tiny for us to be able to explain other than it being a single black hole. Alternatively, there might be a stellar mechanism we simply don’t know about, at least within current physics.

Bottom line: Scientists using the Hubble space telescope have found evidence for an intermediate-mass black hole in the closest globular cluster to Earth, M4.

Via NASA

Read more: A new Goldilocks black hole

Saturn’s moon Enceladus is famous for its huge, active plumes of water vapor. They erupt like geysers at this little moon’s south pole. NASA’s Cassini spacecraft discovered them in 2005. And scientists quickly surmised that the plumes originate from a global ocean below the surface of Saturn’s moon. That subsurface ocean might be inhabited by living things. So the plumes might contain evidence of life. In May 2023, we began to hear that the James Webb Space Telescope (JWST) has now taken a new close look at Enceladus. Webb has observed a new, much larger plume.

The water vapor plumes on Enceladus can be huge, generally speaking. They tower above the moon’s icy surface. Consider that Enceladus itself is only about 314 miles (505 km) wide. The plumes spotted by Cassini were known to be at least as tall as the moon’s diameter. But this new plume – observed by Webb – is the biggest one ever seen, many times the diameter of Enceladus itself. As Sara Faggi, a planetary astronomer at NASA’s Goddard Space Flight Center, said:

It’s immense.

Biggest water plume on Enceladus ever seen

We haven’t seen a statement from scientists about the new plume. And we haven’t seen the Webb image. It apparently hasn’t been released yet.

But Alexandra Witze wrote about the new plume in Nature on May 18, 2023.

And Faggi mentioned the plume and the Webb observations at a conference at the Space Telescope Science Institute in Baltimore, Maryland, on May 17.

While few details were presented at the conference, Faggi said that a new paper will be coming out soon.

Many times Enceladus’ diameter

The water vapor erupts through large cracks in Enceladus’ icy surface. Scientists call these cracks tiger stripes.

The venting was known for sending the water vapor and other particles it contains a long way from Enceladus, out into space. But this newest eruption sent spray from the moon’s interior even farther out, up to many times Enceladus’ diameter of 314 miles (505 km).

Webb was able to observe this plume on November 22, 2022, and scientists have been studying the data sent back ever since.

Cassini analyzed particles in the plume that were relatively close to Enceladus itself. But Webb has the advantage of being able to look at plume particles that travel much farther away from the little moon. The ability to study both will help scientists better understand the plumes and the rich variety of ingredients they contain.

New analysis of Enceladus’ plumes

The analysis of the plume material, to be presented in the forthcoming paper, should be quite interesting. Cassini previously found that the plumes contain water vapor, ice particles, salts, silica, carbon dioxide, ammonia, methane and organic molecules.

Webb observed the plume for only 4.5 minutes, but that was ample time to obtain the data needed. The analysis will provide more details about how much water vapor the plume contained and the temperature. This plume, however, since it is so spread out away from Enceladus, is likely much more diffuse than the plumes Cassini saw (and actually flew through!). That may make it more difficult to determine what kinds of organic molecules were in the plume. Cassini did find a variety of both simple and complex organic molecules during its mission, however. As Witze wrote:

But the plume is likely to be of low density, more like a diffuse, cold cloud than a damp spray. That’s not great news for anyone looking to grab samples from the plume and hoping to find life, because the signs of life might be too sparse to detect. Ice grains seen by Cassini much closer to Enceladus are more likely to have high concentrations of organic particles, says Shannon MacKenzie, a planetary scientist at the Johns Hopkins University Applied Physics Laboratory in Laurel, Maryland.

With that in mind, Webb did find an abundance of intriguing chemicals in the plume. Witze wrote:

JWST also analyzed the spectrum of sunlight reflecting off Enceladus and found evidence of many chemicals, including water and possibly other compounds that could hint at geological or biological activity in the moon’s ocean.

What are they? We’ll have to wait to find out, but as Faggi noted:

We have many more surprises.

Life on Enceladus?

The plumes are of special interest to science because they might contain clues about possible life in Enceladus’ subsurface ocean. The ingredients found so far are tantalizing, although not proof yet that the ocean harbors living organisms.

Cassini did also find evidence suggesting that there are hydrothermal vents on the ocean floor. If so, they could possibly be a source of heat and nutrients, just as they are in oceans on Earth.

Future missions

As of now, there are no confirmed missions going back to Enceladus. But there are ideas on the drawing boards, such as a combination of orbiter and lander called Orbilander. Read the concept study here. A return mission will be essential to find out whether life ever has existed on Enceladus, or still does.

Bottom line: NASA’s Webb Space Telescope has observed the largest water plume on Enceladus ever seen. Details about the analysis results will be published in a new paper.

Via Nature

On July 19 2022, the UK experienced its highest ever temperature. At 40.3℃ (Coningsby, Lincolnshire), the temperature surpassed the previous record of 38.7℃ (Cambridge) – a record that had been set a mere three years previously. My new study shows that this is part of a long-running trend of increasing heat extremes in north-west Europe.

I examined trends in the temperature of the hottest summer day across north-west Europe and compared this to trends in average summer temperatures. My results, published in Geophysical Research Letters, suggest that between 1960 and 2021, north-west Europe has seen its hottest days warm by around 0.6℃ per decade – double the rate at which the region’s average summer days have warmed.

The trend suggests that the region could suffer extremely hot days more often in the future. But this trend isn’t captured in current climate models. While state-of-the-art climate models correctly simulated the trend in average summer temperatures, they failed to capture the enhanced warming of the extremes.

These same climate models are, however, often used to inform impact assessments of climate change. So their inability to simulate the magnitude of trends in extreme temperatures in north-west Europe means that the heat-related impacts of climate change may be underestimated in the short term – and inadequately prepared for as a result.

This is concerning. Infrastructure in north-west Europe is already poorly equipped to deal with extremely hot weather. And extreme heat can have several negative effects on human health and society.

Imported air

The mechanism causing the temperature trends to differ for this region is not yet understood. But the hottest summer days in north-west Europe are often linked to the movement of hot air from over Spain or the Sahara. This was certainly the case in both July last year and July 2019.

Climate change is causing Spain and north Africa to warm faster than north-west Europe. My study found that between 1960 and 2021, the UK warmed by around 0.25℃ per decade compared to more than 0.5℃ per decade for much of Spain. Consequently, plumes of increasingly hot air that are carried north from these regions will bring high temperatures relative to the ambient air temperature of north-west Europe – these temperatures often exceed the threshold to be classified as “extreme”.

Climate models that show Spain and north Africa warming faster than north-west Europe also tend to see a greater rise in heat extremes in north-west Europe relative to mean warming in the future. Although adding further strength to this hypothesis, further work is needed to test the idea more rigorously.

Other possible hypotheses for the enhanced warming of heat extremes include changes to the atmospheric circulation patterns that drive heatwaves. Heatwaves are usually associated with high-pressure “anticyclonic” systems that push warm air northwards. These weather systems are accompanied by clear skies that allow the sun to heat the land.

There is some evidence that the increased occurrence of weather patterns like this could account for the rapid rise in very hot days.

Should we be worried?

The rising intensity of extreme heat in north-west Europe is worrying. Research has found that extreme heat can exacerbate respiratory and cardiovascular diseases and increase the risk of suffering heat stroke. This will put a strain on the health and emergency services.

Much of the infrastructure in the UK – and north-west Europe – is also not designed to deal with extreme heat. In the past, heatwaves have damaged road surfaces and have caused rails to buckle (where they expand and start to curve), leading to severe delays on rail services. On July 19 2022, for example, soaring temperatures meant no trains ran into or out of London King’s Cross rail station.

Homes in the UK also heat up much faster than those in other European countries. According to one study, the temperature inside an average British home will increase by 5℃ in just three hours when the outside temperature is 30℃. That is more than double the rate at which homes across much of western Europe will gain heat.

Yet little is being done to help the same infrastructure cope with even hotter weather in the future. A recent report by the Climate Change Committee, an independent body advising the UK government on its response to climate change, found that the government is not taking sufficient action to adapt to climate change. The report highlighted the need to better heat-proof homes and mitigate wildfire risk as high temperatures become more common.

Over the past 60 years, north-west Europe’s hottest days have become much warmer. These findings indicate that the region is already dealing with the effects of climate change and underline the urgent need to adapt systems and infrastructure to help this area withstand it. From a scientific perspective, we must identify the reasons for the enhanced warming of heat extremes in order to improve current models and find out if this pattern is likely to continue in the future.

Matthew Patterson, Postdoctoral Research Assistant in in Atmospheric Physics, University of Oxford

This article is republished from The Conversation under a Creative Commons license. Read the original article.