One of the most powerful objects in the universe is a radio quasar – a spinning black hole spraying out highly energetic particles. Come too close to one, and you’d get sucked in by its gravitational pull, or burn up from the intense heat surrounding it. But ironically, studying black holes and their jets can give researchers insight into where potentially habitable worlds might be in the universe.

As an astrophysicist, I’ve spent two decades modeling how black holes spin, how that creates jets, and how they affect the environment of space around them.

What are black holes?

Black holes are massive, astrophysical objects that use gravity to pull surrounding objects into them. Active black holes have a pancake-shaped structure around them called an accretion disk, which contains hot, electrically charged gas.

The plasma that makes up the accretion disk comes from farther out in the galaxy. When two galaxies collide and merge, gas is funneled into the central region of that merger. Some of that gas ends up getting close to the newly merged black hole and forms the accretion disk.

There is one supermassive black hole at the heart of every massive galaxy.

Black holes and their disks can rotate, and when they do, they drag space and time with them – a concept that’s mind-boggling and very hard to grasp conceptually. But black holes are important to study because they produce enormous amounts of energy that can influence galaxies.

How energetic a black hole is depends on different factors, such as the mass of the black hole, whether it rotates rapidly, and whether lots of material falls onto it. Mergers fuel the most energetic black holes, but not all black holes are fed by gas from a merger. In spiral galaxies, for example, less gas tends to fall into the center, and the central black hole tends to have less energy.

One of the ways they generate energy is through what scientists call “jets” of highly energetic particles. A black hole can pull in magnetic fields and energetic particles surrounding it, and then as the black hole rotates, the magnetic fields twist into a jet that sprays out highly energetic particles.

Magnetic fields twist around the black hole as it rotates to store energy – kind of like when you pull and twist a rubber band. When you release the rubber band, it snaps forward. Similarly, the magnetic fields release their energy by producing these jets.

These jets can speed up or suppress the formation of stars in a galaxy, depending on how the energy is released into the black hole’s host galaxy.

Rotating black holes

Some black holes, however, rotate in a different direction than the accretion disk around them. This phenomenon is called counterrotation, and some studies my colleagues and I have conducted suggest that it’s a key feature governing the behavior of one of the most powerful kinds of objects in the universe: the radio quasar.

Radio quasars are the subclass of black holes that produce the most powerful energy and jets.

You can imagine the black hole as a rotating sphere, and the accretion disk as a disk with a hole in the center. The black hole sits in that center hole and rotates one way, while the accretion disk rotates the other way.

This counterrotation forces the black hole to spin down and eventually up again in the other direction, called corotation. Imagine a basketball that spins one way, but you keep tapping it to rotate in the other. The tapping will spin the basketball down. If you continue to tap in the opposite direction, it will eventually spin up and rotate in the other direction. The accretion disk does the same thing.

Since the jets tap into the black hole’s rotational energy, they are powerful only when the black hole is spinning rapidly. The change from counterrotation to corotation takes at least 100 million years. Many initially counterrotating black holes take billions of years to become rapidly spinning corotating black holes.

So, these black holes would produce powerful jets both early and later in their lifetimes, with an interlude in the middle where the jets are either weak or nonexistent.

When the black hole spins in counterrotation with respect to its accretion disk, that motion produces strong jets that push molecules in the surrounding gas close together, which leads to the formation of stars.

But later, in corotation, the jet tilts. This tilt makes it so that the jet impinges directly on the gas, heating it up and inhibiting star formation. In addition to that, the jet also sprays X-rays across the galaxy. Cosmic X-rays are bad for life because they can harm organic tissue.

For life to thrive, it most likely needs a planet with a habitable ecosystem, and clouds of hot gas saturated with X-rays don’t contain such planets. So, astronomers can instead look for galaxies without a tilted jet coming from its black hole. This idea is key to understanding where intelligence could potentially have emerged and matured in the universe.

Black holes as a guide

By early 2022, I had built a black hole model to use as a guide. It could point out environments with the right kind of black holes to produce the greatest number of planets without spraying them with X-rays. Life in such environments could emerge to its full potential.

Where are such conditions present? The answer is low-density environments where galaxies had merged about 11 billion years ago.

These environments had black holes whose powerful jets enhanced the rate of star formation, but they never experienced a bout of tilted jets in corotation. In short, my model suggested that theoretically, the most advanced extraterrestrial civilization would have likely emerged on the cosmic scene far away and billions of years ago.

David Garofalo, Professor of Physics, Kennesaw State University

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

Cataract surgery is one of the most popular and commonly performed procedures in the world. The vast majority of patients have excellent outcomes with few complications.

Here are the numbers:

• By age 80, over half of all Americans have cataracts.

• Close to 4 million cataract surgeries are performed in the U.S. every year.

• Over 90% of patients have 20/20 vision with glasses after surgery, although those with other eye conditions may not do as well, including those with glaucoma, a progressive disease typically associated with elevated pressure within the eye; diabetic retinopathy, which ultimately can cause leakage in the retinal tissues; and macular degeneration, a disease that is typically related to age.

• The rate of post-surgery infection from endophthalmitis is less than 0.1%.

As ophthalmologists who have performed thousands of these procedures, we know that many patients have misconceptions about both cataracts and the surgery. For example, some think a cataract is a growth on the eye’s surface.

We like to compare a cataract with the frosted glass of a bathroom window, where light can be transmitted but details cannot. Or when turbulence from a storm causes normally clear water in the ocean to become murky. In much the same way, the eye’s once transparent lens becomes cloudy.

About the surgery

Cataract surgery removes the clouded lens of the eye and replaces it with a new, clear lens to restore your vision. Most patients report the procedure is painless.

It’s typically an elective surgery that is performed on an outpatient basis. The patient is often awake, under local anesthesia, with sedation similar to that used for dental procedures. We like to say patients receive the equivalent of three margaritas in their IV.

Numbing drops are then applied to the eye’s surface, along with an anesthetic inside the eye. Patients with claustrophobia, or movement disorders such as Parkinson’s disease, may not be suitable candidates for awake surgeries and require general anesthesia.

Before surgery, patients receive dilating drops to make the pupil as large as possible. The surgeon makes a tiny incision, usually with a small pointed scalpel, between the clear and white part of the eye to gain access to the lens capsule, a thin membrane similar in thickness to a plastic produce bag at the grocery store.

This capsule is suspended by small fibers called zonules, which are arranged like the springs that suspend a trampoline from a frame. The surgeon then creates a small opening in the capsule, called a capsulotomy, to gain access to the cataract. The cataract is then broken into smaller parts so they are removable through the small incision.

This is similar to a tiny jackhammer, breaking the large lens into smaller pieces for removal. That sounds scary, but it’s painless. Ultrasound emulsifies the lens and vacuum power then aspirates it from the eye.

Laser-assisted cataract surgery has been found to have similar outcomes to traditional cataract surgery.

Complications are rare

Serious complications, such as postoperative infection, bleeding in the eye or a postoperative retinal detachment are rare; they occur in approximately 1 in 1,000 cases. But even in many of these situations, appropriate management can salvage useful vision.

Capsular complications deserve additional discussion. According to some studies, they occur in up to 2% of cases. If a hole or tear of the posterior capsule is encountered during cataract surgery, the clear gel in the vitreous – the back chamber of the eye – may be displaced into the front chamber of the eye.

If that happens, the gel must be removed at the time of the cataract surgery. This will reduce the likelihood of additional postoperative complications, but those who have the procedure, known as a vitrectomy, have an increased risk for additional complications, including postoperative infections and postoperative swelling.

After the surgery

Patients usually go home right after the procedure. Most surgery centers require that the patient have someone drive them home, more for the anesthesia rather than the surgery. Patients begin applying postoperative drops that same day and must wear an eye shield at bedtime for a few weeks after surgery.

Patients should keep the eye clean and avoid exposure to dust, debris and water. They should try not to bend over and should avoid heavy lifting or straining in the first week or so after surgery. Lifting or straining can cause a surge of blood pressure to the face and eye. Known as a choroidal hemorrhage, it can lead to bleeding into the wall of the eye and be devastating to vision.

Things that cause only moderate increases in heart rate such as walking are OK. Routine postoperative examinations are usually completed the day after surgery, about a week after surgery and about a month after surgery.

A choice of lens

The plastic lens used to replace the cataract, or intraocular lens, requires careful sizing for optimal results and a nuanced discussion between patient and surgeon.

Early intraocular lens technologies were monofocal, and most patients with these lenses chose distance correction and used reading glasses for near tasks. This is still the preferred approach for approximately 90% of patients having cataract surgery today.

Recent advances have led to intraocular lenses that offer multifocality – the opportunity to have near as well as distance vision, without glasses. Some multifocal lenses are even in the trifocal category, which includes distance, near, and intermediate vision, the latter of which in recent years has become very important for computer and phone use.

Most patients with these advanced technology multifocal lenses are happy with them. However, a small percentage of patients with multifocal lenses can be so bothered by visual disturbances – notably night glare and halos around light sources in the dark – that they request removal of the multifocal lens to exchange it for a standard intraocular lens. These exchanges are a reasonable option for such situations and offer relief for most affected patients.

Determining who’s an ideal candidate for a multifocal intraocular lens is an area of active research. Most clinicians would recommend against such a lens for a patient with a detail-oriented personality. Such patients tend to fixate on the shortcomings of these lenses despite their potential advantages.

As with many technologies, current generation advanced technology intraocular lenses are much better than their predecessors. Future offerings are likely to offer improved vision and fewer side effects than those available today.

But these newer lenses are often not reimbursed by insurance companies and often entail substantial out-of-pocket costs for patients.

Deciding on what type of lens is best for you can be complicated. Fortunately, except in unusual circumstances, such as when a cataract develops after trauma to the eye, there is seldom a hurry for adult cataract surgery.

Allan Steigleman, Associate Professor of Ophthalmology, University of Florida and Elizabeth M. Hofmeister, Associate Professor of Surgery, Uniformed Services University of the Health Sciences

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