Black holes have different diets

Black holes are some of the most mysterious and powerful objects in the universe. They grow larger as they basically swallow everything they come across, including dust, stars, planets, and even other black holes. However, a new study shows that black holes have different diets and eating habits.

Some black holes are messy eaters, swallowing huge chunks of matter at once, producing bright bursts of light. Others are much more sophisticated eaters, consuming their food in a slow and steady stream, creating barely a ripple in the cosmic pond.

Scientists have been trying to understand these differences for years. Now, thanks to data from NASA's retired Spitzer Space Telescope, they have revealed the mystery of how some black holes, such as the one at the center of our neighboring galaxy Andromeda, maintain their eating habits.

Black holes feed on streams of dust

Researchers used the Spitzer Space Telescope's infrared imaging technology to probe the core of the Andromeda galaxy. This investigation revealed extensive dust streams that extend thousands of light-years, directed toward the supermassive black hole at the center of the galaxy.

These observations of dust activity are important because they help explain the processes by which a black hole continuously feeds incoming material in a steady, suppressed manner.

black hole buffet

When a black hole consumes enough matter, such as a star or gas cloud, the interaction is visually dramatic. The immense gravitational pull of the black hole rapidly heats this material to extremely high temperatures as it approaches the event horizon – the boundary beyond which nothing can survive.

As the material accelerates and heats up, it emits huge amounts of radiation in different wavelengths of the electromagnetic spectrum. This emission can be so intense that it sometimes outshines the collective light of the entire galaxy, creating what are known as quasars or active galactic nuclei.

However, the supermassive black holes at the centers of the Milky Way and Andromeda exhibit much quieter behavior. Unlike more active black holes, these do not display the same dramatic flashes of brightness.

The light emitted from these black holes is very slow and remains constant over time. This shows that they do not engage in sporadic consumption by large groups of people. Instead, they appear to be constantly collecting small amounts of content.

This method of consumption is less disruptive and does not cause the same level of loud outbursts, so they are classified as some of the quietest eaters in the universe. Their feeding process, which is characterized by the ingestion of smaller, more consistent streams of matter, contrasts sharply with the more predatory and episodic feeding habits seen in other galactic centres.

The secret ingredient in the black hole's diet

A study published earlier this year proposed a theory to explain it. The researchers suggested that these cool black holes have a diet that consists of a constant stream of gas and dust.

They used computer simulations to model how gas and dust would behave near a supermassive black hole. The simulations showed that a steady flow of material could form a spinning disk around the black hole, providing a constant source of nourishment.

However, this theory comes with a twist. The streams feeding a black hole cannot be too large or too small. If they're too big, they may break apart and fall into the black hole in unpredictable clumps, causing messy bursts of light. But if they are too small, the black hole won't get enough to eat and will begin to shrink.

Spitzer to the rescue

The researchers compared their simulations to actual observations from Spitzer and its cousin, the Hubble Space Telescope. They found dusty spirals in Andromeda that matched the estimated size and flow rate needed to feed a cool black hole.

These dusty tendrils may be the black hole's own buffet line, constantly replenished to satisfy its insatiable appetite. “This is a great example of scientists re-examining old data to reveal new insights,” said Almudena Prieto, an astrophysicist who was not involved in the study. “We have 20 years of data telling us things that we didn't recognize when we first collected it.”

An in-depth look at Andromeda

Launched in 2003, Spitzer was a marvel of engineering. It was specifically designed to view the universe in infrared light, which is invisible to our eyes. Different infrared wavelengths reveal different characteristics of celestial objects. Hot, bright objects like stars appear brighter in some wavelengths, while cooler objects like dust clouds appear brighter in other wavelengths.

By varying these wavelengths, astronomers can essentially peel back the layers of the galaxy, revealing its hidden structure. In the case of Andromeda, this led to a stunning view of the black hole's vital diet.

Unlike our galaxy, which has distinctive spiral arms, Andromeda is dominated by a large ring of dust. There is also a strange gap in the ring, possibly caused by a smaller galaxy rotating a little too close.

Andromeda's proximity to Earth makes it a prime target for astronomical study. It is the nearest large galaxy to our Milky Way, and to the naked eye it will appear six times wider than the Moon. Even with a powerful telescope like Spitzer, capturing a detailed image of Andromeda requires 11,000 separate snapshots.


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