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Scientists Discover Way to Send Information into Black Holes Without Using Energy

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How Supermassive Black Holes Get Their Metal-Rich Fuel?

Supermassive black holes (SMBHs) are some of the most powerful objects in the universe. They can be millions or even billions of times more massive than the Sun and are found at the centers of large galaxies.

But an important question has puzzled scientists for years: Where does the gas that feeds these giant black holes come from?

A new study by Kwak and colleagues provides an interesting answer. Using 30 detailed computer simulations of massive galaxies, the researchers followed the journeys of individual gas particles through cosmic history. Their goal was to understand where black-hole-feeding gas comes from and how its chemical composition changes before it reaches the black hole.

The results show that much of this gas may actually come from stars inside the galaxy itself.

Black Holes and Galaxies Grow Together

Supermassive black holes do not evolve separately from their galaxies. Scientists have found strong links between the mass of a central black hole and the properties of its host galaxy.

For example, larger galaxies often contain larger central black holes. This suggests that the growth of galaxies and their black holes is closely connected.

Gas is an important part of this relationship. When gas moves toward the center of a galaxy, some of it can eventually reach the region around the black hole. The black hole can then pull in this material and grow larger.

When a black hole actively consumes large amounts of gas, it can become extremely bright and form an active galactic nucleus, or AGN.

However, the black hole does not simply consume gas without affecting its surroundings. The energy released by an active black hole can heat and push away gas. This process, called AGN feedback, can affect star formation and influence how the entire galaxy develops.

Scientists Followed the Journey of Gas

To understand the source of the gas, Kwak and the team used 30 high-resolution cosmological simulations.

These simulations were designed to follow the growth of massive galaxies and their central black holes over billions of years.

The galaxies studied have stellar masses between about 10^10.9 and 10^11.9 times the mass of the Sun. Their central black holes have masses between about 10^8.5 and 10^9.7 solar masses.

The researchers used a powerful method called particle tracing. Instead of looking only at where gas is located at a particular time, they followed individual gas particles and reconstructed their journeys.

This allowed them to answer questions such as:

  • Where did the gas originally come from?

  • Did it come from stars, other galaxies, or intergalactic space?

  • How did its chemical composition change?

  • How long did it spend inside the galaxy before reaching the black hole?

The researchers divided the gas into four main groups.

Four Types of Gas

1. Recycled gas

This is gas that originally came from stars inside the main galaxy.

Stars do not keep all their material forever. During their lives and especially during their later stages, they release gas back into space through stellar winds and explosions.

This returned material contains many heavy elements created inside stars.

2. Early gas

This gas entered the main halo during the early stages of the galaxy's formation.

It became part of the galaxy's gas supply very early in cosmic history.

3. External gas

This gas came from outside the main galaxy. It could have originated in other galaxies or smaller structures called subhalos.

4. Smooth gas

This gas came directly from the larger intergalactic environment rather than from another galaxy.

By separating the gas into these groups, scientists could understand which sources are most important for feeding supermassive black holes.

Stars Are a Major Source of Black-Hole Fuel

The most important discovery is that recycled gas from stars makes up the largest part of the gas supply reaching the black holes.

This is especially important in massive galaxies that contain many old stars.

Even when stars are no longer actively forming, they can continue to lose material. Some of this material comes from aging stars known as asymptotic giant branch (AGB) stars. Supernova explosions also return enriched material to the surrounding gas.

This means stars are not simply objects that consume gas to form. They also return chemically enriched material to their surroundings.

Some of this recycled material can eventually travel toward the center of the galaxy and feed the supermassive black hole.

Gas Can Become Richer in Metals

The study also found that gas from outside the galaxy can become chemically enriched before reaching the black hole.

When external gas enters a galaxy, it can mix with gas that has already been enriched by stars and supernovae.

This process is known as chemical pre-processing.

In simple terms, the gas can become richer in heavy elements while it is still traveling through the galaxy.

Therefore, gas does not necessarily reach the black hole with the same chemical composition it had when it first entered the galaxy.

The galaxy acts as a kind of natural mixing and enrichment system.

Why Are Quasars So Rich in Heavy Elements?

One of the biggest mysteries in astronomy is the high metallicity observed around powerful quasars.

Astronomers have found that the gas around many bright quasars contains large amounts of heavy elements. This is surprising because some quasars are seen when the universe was very young.

Scientists might expect young galaxies to contain less heavy elements because elements such as iron and magnesium are produced by stars over time.

The new simulations provide a possible explanation.

Massive galaxies can develop chemically rich central gas reservoirs relatively early. Once these reservoirs become enriched, future gas flowing toward the black hole can also be metal rich.

This means the high metallicity around quasars may be a natural result of the way galaxies grow and recycle material.

Iron and Magnesium Tell the Story

The researchers also studied chemical ratios such as [Fe/H], which describes the amount of iron compared with hydrogen, and [Mg/Fe], which compares magnesium with iron.

The amount of iron in gas reaching the black hole shows only weak changes over cosmic time.

In other words, the gas feeding these black holes can remain highly enriched even as the universe becomes older.

The magnesium-to-iron ratio shows a small decrease toward the present day. Scientists believe this is connected to the growing contribution of iron from Type Ia supernovae, which become more important as older stellar populations evolve.

These chemical clues help scientists understand the history of the gas before it reaches the black hole.

Black Holes Get Access to Special Gas

Another important result is that the gas reaching the black hole can be more metal rich than the average gas in the galaxy, especially around 1–3 billion years after the Big Bang.

This suggests that black holes are not simply consuming random gas from their host galaxies.

Instead, they can gain access to gas that has spent time in the central parts of the galaxy, where chemical enrichment is stronger.

The gas that finally reaches the black hole therefore carries a record of the galaxy's history.

A New Picture of Black-Hole Growth

The study gives scientists a clearer picture of how supermassive black holes receive their fuel.

The process begins with stars, galaxies, and the wider cosmic environment. Stars produce heavy elements and later return enriched material to the surrounding gas. That material can mix with gas coming from outside the galaxy.

Over time, some of this enriched gas moves toward the center and becomes available to the black hole.

This creates a direct connection between stellar evolution, chemical enrichment, galaxy growth, and black-hole growth.

Most importantly, the study shows that the metal-rich environment around supermassive black holes does not necessarily require unusual processes. It can naturally develop through ordinary galaxy evolution and the recycling of material from stars.

The Bigger Picture

Supermassive black holes may look like isolated cosmic giants, but their growth is deeply connected to the life cycle of stars and galaxies.

The gas they consume can carry the chemical fingerprints of stars that lived and died long before the gas reached the black hole.

The research by Kwak and colleagues therefore reveals an important part of the cosmic story: stars may help feed the very black holes that sit at the hearts of galaxies.

By following gas from its original source to the black hole, scientists are getting closer to understanding how galaxies and their central black holes have grown together across billions of years.

Reference: Dongyun Kwak, Ena Choi, Hannah Jhee, Rachel S. Somerville, Thorsten Naab, Michaela Hirschmann, Jaejin Shin, Jong-Hak Woo, "Recycled Gas Dominates the Metal-rich Fuel of Supermassive Black Holes", Arxiv, 2026. https://arxiv.org/abs/2608.12462

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