The hottest topic in astronomy is what the little red dot (LRD) hidden in JWST images actually is.

Everyone agrees that they are high –redshift It’s a compact yet bright (and therefore distant) system, but anything more is still up for debate.

A leading theory is that its brightness comes from material raining down on a supermassive black hole at the center of a small galaxy, but it’s hard to understand how such a beast could grow.

Adding to the mystery, if accretion to a black hole is involved, the dots will appear faint in X-rays and radio waves, both of which would normally be bright.

Get to the bottom of the mystery

While theorists are considering ever more outlandish ideas, observers are looking for ways to constrain what these objects are actually like.

So I was pleased to see a paper by a large international team led by Peking University’s Zijian Zhang that explored this unusual detail in detail.

The target is a galaxy cluster known as RXC J2211-0350. This acts as a foreground light source, and behind it are two LRDs whose light is bent by gravity as it passes through the cluster. This effect is known as “LRD”. gravity lens.

According to the paper, this lensing effect magnifies dots that are farther away by several times. But for one of them, the results are more dramatic.

1 dot, 4 images

Due to its position, the light from the small red dot RX1 is split into four separate images, or Einstein crosses.

And what’s especially interesting is that the shape of the lens causes the light to travel a slightly different distance to produce each image. So you’ll actually see four snapshots of the dot taken at slightly different times.

By modeling clusters, the researchers estimate that the difference between the newest and oldest images is about 130 years.

Subtle changes in brightness and color between images show how these objects have evolved over more than a century.

So what do these changes tell us about the source of the dot’s brightness?

The researchers suggest that the supermassive black hole believed to be at the center of RX1 may have an envelope of hot gas surrounding it, heated by accretion onto the central object, causing it to pulsate like a giant variable star.

These pulses would explain the changes in brightness we see.

The authors explain that not all small red dots exhibit similar behavior. As with variable stars, whether the pulsed mode can be maintained depends on the exact temperature and pressure of the gas.

But in the case of RX1, this is a convincing argument if you believe that the brightness changes follow a smooth periodic pattern. The paper suggests that a period of 32 years between maximum values ​​fits the data.

If this model is correct, follow-up observations of various dot images over the next few years should reveal steady changes in brightness.

If some other mechanism is at work, for example, if the brightness is changing because different amounts of matter fall into the black hole at different times, we should see more random changes in brightness.

Either way, RX1 will play a major role in understanding these mysterious and exciting new objects.

Chris Lintott was reading A century of small red dot fluctuations reveals black hole envelope via giant Einstein cross According to Zijian Zhang et al. Read online at arxiv.org/abs/2512.05180.

This article was published in the February 2026 issue of BBC Sky at Night Magazine.