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Black holes have different diets - and some are picky eaters

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

Some black holes are messy eaters, gobbling up huge chunks of matter at once, causing bright outbursts of light. Others are much more refined diners, consuming their diet in a slow and steady stream, barely causing 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 may have uncovered the secret to how some black holes, like the one at the center of our neighboring galaxy Andromeda, maintain their picky eating habits.

Black hole’s diet via dust streams

Researchers employed the infrared imaging technology of the Spitzer Space Telescope to examine the core of the Andromeda galaxy. This investigation revealed extensive dust streams that extend for thousands of light-years, directing towards the supermassive black hole at the galaxy’s center.

These observations of dust movements are crucial as they help explain the processes by which the black hole continuously feeds on incoming material in a steady, subdued manner.

Black hole buffet

When a black hole consumes a substantial amount of matter, such as a star or a 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 escape.

As the material accelerates and heats up, it emits a vast amount of radiation across various wavelengths of the electromagnetic spectrum. This emission can be so intense that it sometimes outshines the collective light of an entire galaxy, creating what is known as a quasar or an active galactic nucleus.

However, the supermassive black holes located 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 flares of brightness.

The light emitted from these black holes is notably faint and remains consistent over time. This suggests that they are not engaging in the sporadic consumption of large masses. Instead, they appear to be steadily accreting smaller quantities of material.

This method of consumption is less disruptive and does not lead to the same level of radiant outburst, hence their categorization as some of the quietest eaters in the universe. Their feeding process, characterized by the ingestion of smaller, more consistent streams of matter, contrasts sharply with the more violent and episodic feeding habits seen in other galactic centers.

Secret ingredient in black hole’s diet

A study published earlier this year proposed a theory to explain this. The researchers suggested that these quiet black holes have a diet that consists of a continuous 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 swirling disk around the black hole, providing a constant source of nourishment.

This theory, however, comes with a twist. The streams feeding the black hole can’t be too big or too small. If they’re too large, they could break apart and fall into the black hole in unpredictable clumps, causing those messy outbursts of light. But if they’re too small, the black hole wouldn’t get enough to eat and would start 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 predicted size and flow rate needed to feed a quiet black hole. 

These dusty tendrils could be the black hole’s personal buffet line, constantly replenished to satisfy its insatiable appetite. “This is a great example of scientists reexamining old data to reveal new insights,” said Almudena Prieto, an astrophysicist involved in the study. “We have 20-year-old data telling us things we didn’t recognize when we first collected it.”

Deeper look into Andromeda

Launched in 2003, Spitzer was a marvel of engineering. It was specifically designed to see the universe in infrared light, which is invisible to our eyes. Different infrared wavelengths reveal different features of celestial objects. Hot, glowing objects like stars show up brightly in certain wavelengths, while cooler objects like dust clouds appear in others.

By separating these wavelengths, astronomers can essentially peel back the layers of a galaxy, revealing its hidden structure. In the case of Andromeda, this revealed a surprising view of the black hole’s vital diet. 

Unlike our Milky Way, which has distinct spiral arms, Andromeda is dominated by a large ring of dust. This ring also has a curious gap, likely caused by a smaller galaxy that wandered a little too close.

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


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