Singularity HUB

Black holes are known for ferocious gravitational fields. Anything wandering too close, even light, will be swallowed up. But other forces may be at play too.

In 2021, astronomers used the Event Horizon Telescope (EHT) to make a polarized image of the enormous black hole at the center of the galaxy M87. The image showed an organized swirl of magnetic fields threading the matter orbiting the object. M87*, as the black hole is known, is nearly 1,000 times bigger than our own galaxy’s central black hole, Sagittarius A* (Sgr A*) and is dining on the equivalent of a few suns per year. With its comparatively modest size and appetite—Sgr A* is basically fasting at the moment—scientists wondered if our galaxy’s black hole would have strong magnetic fields too.

Now, we know.

In the first polarized image of Sgr A*, released alongside two papers published today (here and here), EHT scientists say the black hole has strong magnetic fields akin to those seen in M87*. The image depicts a fiery whirlpool (the disc of material falling into Sgr A*) circling the drain (the black hole’s shadow) with magnetic field lines woven throughout.

In contrast to unpolarized light, polarized light is oriented in only one direction. Like a pair of quality sunglasses, magnetized regions in space polarize light too. These polarized images of the two black holes therefore map out their magnetic fields.

And surprisingly, they’re similar.

Side-by-side polarized images of supermassive black holes M87* and Sagittarius A*. Image Credit: EHT Collaboration

“With a sample of two black holes—with very different masses and very different host galaxies—it’s important to determine what they agree and disagree on,” Mariafelicia De Laurentis, EHT deputy project scientist and professor at the University of Naples Federico II, said in a press release. “Since both are pointing us toward strong magnetic fields, it suggests that this may be a universal and perhaps fundamental feature of these kinds of systems.”

Making the image was no simple task. Compared to M87*, whose disc is larger and moves relatively slowly, imaging Sgr A* is like trying to photograph a cosmic toddler—its material is always in motion, reaching nearly the speed of light. The scientists had to use new tools in addition to those that yielded the polarized image of M87* and weren’t even sure the image would be possible.

Such technical feats take enormous teams of scientists organized across the globe. The first three pages of each new paper are dedicated to authors and affiliations. In addition, the EHT itself spans the world. Astronomers stitch observations made by eight telescopes into a virtual Earth-sized telescope capable of resolving objects the apparent size of a donut on the moon as viewed from the surface of our planet.

The EHT team plans to make more observations—the next round for Sgr A* begins next month—and add telescopes on Earth and space to increase the quality and breadth of the images. One outstanding question is whether Sgr A* has a jet of material shooting out from its poles like M87* does. The ability to make movies of the black hole later this decade—which should be spectacular—could resolve the mystery.

“We expect strong and ordered magnetic fields to be directly linked to the launching of jets as we observed for M87*,” Sara Issaoun, research co-leader and a fellow at Harvard & Smithsonian’s Center for Astrophysics, told Space.com. “Since Sgr A*, with no observed jet, seems to have a very similar geometry, perhaps there is also a jet lurking in Sgr A* waiting to be observed, which would be super exciting!”

The discovery of a jet, added to strong magnetic fields, would mean these features may be common to supermassive black holes across the spectrum. Learning more about their features and behavior can help scientists piece together a better picture of how galaxies, including the Milky Way, evolve over eons in tandem with the black holes at their hearts.

Image Credit: EHT Collaboration

The human genetic blueprint is deceptively simple. Our genes are tightly wound into 46 X-shaped structures called chromosomes. Crafted by evolution, they carry DNA and replicate when cells divide, ensuring the stability of our genome over generations.

In 1997, a study torpedoed evolution’s playbook. For the first time, a team created an artificial human chromosome using genetic engineering. When delivered into a human cell in a petri dish, the artificial chromosome behaved much like its natural counterparts. It replicated as cells divided, leading to human cells with 47 chromosomes.

Rest assured, the goal wasn’t to artificially evolve our species. Rather, artificial chromosomes can be used to carry large chunks of human genetic material or gene editing tools into cells. Compared to current delivery systems—virus carriers or nanoparticles—artificial chromosomes can incorporate far more synthetic DNA.

In theory, they could be designed to ferry therapeutic genes into people with genetic disorders or add protective ones against cancer.

Yet despite over two decades of research, the technology has yet to enter the mainstream. One challenge is that the short DNA segments linking up to form the chromosomes stick together once inside cells, making it difficult to predict how the genes will behave.

This month, a new study from the University of Pennsylvania changed the 25-year-old recipe and built a new generation of artificial chromosomes. Compared to their predecessors, the new chromosomes are easier to engineer and use longer DNA segments that don’t clump once inside cells. They’re also a large carrier, which in theory could shuttle genetic material roughly the size of the largest yeast chromosome into human cells.

“Essentially, we did a complete overhaul of the old approach to HAC [human artificial chromosome] design and delivery,” study author Dr. Ben Black said in a press release.

“The work is likely to reinvigorate efforts to engineer artificial chromosomes in both animals and plants,” wrote the University of Georgia’s Dr. R. Kelly Dawe, who was not involved in the study.

Shape of You

Since 1997, artificial genomes have become an established  biotechnology. They’ve been used to rewrite DNA in bacteria, yeast, and plants, resulting in cells that can synthesize life-saving medications or eat plastic. They could also help scientists better understand the functions of the mysterious DNA sequences littered throughout our genome.

The technology also brought about the first synthetic organisms. In late 2023, scientists revealed yeast cells with half their genes replaced by artificial DNA—the team hopes to eventually customize every single chromosome. Earlier this year, another study reworked parts of a plant’s chromosome, further pushing the boundaries of synthetic organisms.

And by tinkering with the structures of chromosomes—for example, chopping off suspected useless regions—we can better understand how they normally function, potentially leading to treatments for diseases.

The goal of building human artificial chromosomes isn’t to engineer synthetic human cells. Rather, the work is meant to advance gene therapy. Current methods for carrying therapeutic genes or gene editing tools into cells rely on viruses or nanoparticles. But these carriers have limited cargo capacity.

If current delivery vehicles are like sailboats, artificial human chromosomes are like cargo ships, with the capacity to carry a far larger and wider range of genes.

The problem? They’re hard to build. Unlike bacteria or yeast chromosomes, which are circular in shape, our chromosomes are like an “X.” At the center of each is a protein hub called the centromere that allows the chromosome to separate and replicate when a cell divides.

In a way, the centromere is like a button that keeps fraying pieces of fabric—the arms of the chromosome—intact. Earlier efforts to build human artificial chromosomes focused on these structures, extracting DNA letters that could express proteins inside human cells to anchor the chromosomes. However, these DNA sequences rapidly grabbed onto themselves like double-sided tape, ending in balls that made it difficult for cells to access the added genes.

One reason could be that the synthetic DNA sequences were too short, making the mini-chromosome components unreliable. The new study tested the idea by engineering a far larger human chromosome assembly than before.

Eight Is the Lucky Number

Rather than an X-shaped chromosome, the team designed their human artificial chromosome as a circle, which is compatible with replication in yeast. The circle packed a hefty 760,000 DNA letter pairs—roughly 1/200 the size of an entire human chromosome.

Inside the circle were genetic instructions to make a sturdier centromere—the “button” that keeps the chromosome structure intact and can make it replicate. Once expressed inside a yeast cell, the button recruited the yeast’s molecular machinery to build a healthy human artificial chromosome.

In its initial circular form in yeast cells, the synthetic human chromosome could then be directly passed into human cells through a process called cell fusion. Scientists removed the “wrappers” around yeast cells with chemical treatments, allowing the cells’ components—including the artificial chromosome—to merge directly into human cells inside petri dishes.

Like benevolent extraterrestrials, the added synthetic chromosomes happily integrated into their human host cells. Rather than clumping into noxious debris, the circles doubled into a figure-eight shape, with the centromere holding the circles together. The artificial chromosomes happily co-existed with native X-shaped ones, without changing their normal functions.

For gene therapy, it’s essential that any added genes remain inside the body even as cells divide. This perk is especially important for fast-dividing cells like cancer, which can rapidly adapt to therapies. If a synthetic chromosome is packed with known cancer-suppressing genes, it could keep cancers and other diseases in check throughout generations of cells.

The artificial human chromosomes passed the test. They recruited proteins from the human host cells to help them spread as the cells divided, thus conserving the artificial genes over generations.

A Revival

Much has changed since the first human artificial chromosomes.

Gene editing tools, such as CRISPR, have made it easier to rewrite our genetic blueprint. Delivery mechanisms that target specific organs or tissues are on the rise. But synthetic chromosomes may be regaining some of the spotlight.

Unlike viral carriers, the most often used delivery vehicle for gene therapies or gene editors, artificial chromosomes can’t tunnel into our genome and disrupt normal gene expression—making them potentially far safer.

The technology has vulnerabilities though. The engineered chromosomes are still often lost when cells divide. Synthetic genes placed near the centromere—the “button” of the chromosome—may also disrupt the artificial chromosome’s ability to replicate and separate when cells divide.

But to Dawe, the study has larger implications than human cells alone. The principles of re-engineering centromeres shown in this study could be used for yeast and potentially be “applicable across kingdoms” of living organisms.

The method could help scientists better model human diseases or produce drugs and vaccines. More broadly, “It may soon be possible to include artificial chromosomes as a part of an expanding toolkit to address global challenges related to health care, livestock, and the production of food and fiber,” he wrote.

Image Credit: Warren Umoh / Unsplash

Dark matter is a ghostly substance that astronomers have failed to detect for decades, yet which we know has an enormous influence on normal matter in the universe, such as stars and galaxies. Through the massive gravitational pull it exerts on galaxies, it spins them up, gives them an extra push along their orbits, or even rips them apart.

Like a cosmic carnival mirror, it also bends the light from distant objects to create distorted or multiple images, a process which is called gravitational lensing.

And recent research suggests it may create even more drama than this, by producing stars that explode.

For all the havoc it plays with galaxies, not much is known about whether dark matter can interact with itself, other than through gravity. If it experiences other forces, they must be very weak, otherwise they would have been measured.

A possible candidate for a dark matter particle, made up of a hypothetical class of weakly interacting massive particles (or WIMPs), has been studied intensely, so far with no observational evidence.

Recently, other types of particles, also weakly interacting but extremely light, have become the focus of attention. These particles, called axions, were first proposed in late 1970s to solve a quantum problem, but they may also fit the bill for dark matter.

Unlike WIMPs, which cannot “stick” together to form small objects, axions can do so. Because they are so light, a huge number of axions would have to account for all the dark matter, which means they would have to be crammed together. But because they are a type of subatomic particle known as a boson, they don’t mind.

In fact, calculations show axions could be packed so closely that they start behaving strangely—collectively acting like a wave—according to the rules of quantum mechanics, the theory which governs the microworld of atoms and particles. This state is called a Bose-Einstein condensate, and it may, unexpectedly, allow axions to form “stars” of their own.

This would happen when the wave moves on its own, forming what physicists call a “soliton,” which is a localized lump of energy that can move without being distorted or dispersed. This is often seen on Earth in vortexes and whirlpools, or the bubble rings that dolphins enjoy underwater.

The new study provides calculations which show that such solitons would end up growing in size, becoming a star, similar in size to, or larger than, a normal star. But finally, they become unstable and explode.

The energy released from one such explosion (dubbed a “bosenova”) would rival that of a supernova (an exploding normal star). Given that dark matter far outweighs the visible matter in the universe, this would surely leave a sign in our observations of the sky. We have yet to find such scars, but the new study gives us something to look for.

An Observational Test

The researchers behind the study say that the surrounding gas, made of normal matter, would absorb this extra energy from the explosion and emit some of it back. Since most of this gas is made of hydrogen, we know this light should be in radio frequencies.

Excitingly, future observations with the Square Kilometer Array radio telescope may be able to pick it up.

Artist’s impression of the SKA telescope. Image Credit: Wikipedia, CC BY-SA

So, while the fireworks from dark star explosions may be hidden from our view, we might be able to find their aftermath in the visible matter. What’s great about this is that such a discovery would help us work out what dark matter is actually made of—in this case, most likely axions.

What if observations do not detect the predicted signal? That probably won’t rule out this theory completely, as other “axion-like” particles are still possible. A failure of detection may indicate, however, that the masses of these particles are very different, or that they do not couple with radiation as strongly as we thought.

In fact, this has happened before. Originally, it was thought that axions would couple so strongly that they would be able to cool the gas inside stars. But since models of star cooling showed stars were just fine without this mechanism, the axion coupling strength had to be lower than originally assumed.

Of course, there is no guarantee that dark matter is made of axions. WIMPs are still contenders in this race, and there are others too.

Incidentally, some studies suggest that WIMP-like dark matter may also form “dark stars.” In this case, the stars would still be normal (made of hydrogen and helium), with dark matter just powering them.

These WIMP-powered dark stars are predicted to be supermassive and to live only for a short time in the early universe. But they could be observed by the James Webb Space Telescope. A recent study has claimed three such discoveries, although the jury is still out on whether that’s really the case.

Nevertheless, the excitement about axions is growing, and there are many plans to detect them. For example, axions are expected to convert into photons when they pass through a magnetic field, so observations of photons with a certain energy are targeting stars with magnetic fields, such as neutron stars, or even the sun.

On the theoretical front, there are efforts to refine the predictions for what the universe would look like with different types of dark matter. For example, axions may be distinguished from WIMPs by the way they bend the light through gravitational lensing.

With better observations and theory, we are hoping that the mystery of dark matter will soon be unlocked.

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

Image Credit: ESA/Webb, NASA & CSA, A. Martel