The Week in Space and Physics: The Lost Sisters of the Pleiades

On the stars of the Pleiades, a superflare from a black hole, the second flight of New Glenn, and the aurora.

The Pleiades, captured by Starhopper and shared under CC BY-SA 4.0.

Of all the clusters of stars in the night sky, the Pleiades are perhaps the most famous. Humans have watched them for thousands of years. Ancient paintings of them on cave walls might represent our first forays into astronomy and science, or at least into the art of tracking the seasons and the flows of time.

Naturally, then, there are a great number of stories about them. Cultures across the world have told how the stars of the Pleiades were once sisters fleeing from peril, and that to save them the gods lofted them into the sky and affixed them there for all eternity. But in many of these tales one of the sisters is lost, and so today we see only six stars where once there were seven.

So widespread is this story, even across groups of people separated by vast distances, that some think it may be one of the oldest myths of our species. And indeed, over the past hundred thousand years one of the stars really has disappeared. It has drifted behind another, and to human eyes these two now appear as one.

In time, the sisters of the Pleiades will lose each other entirely. The cluster from which they were born, roughly one hundred million years ago, is dissolving. Like all such clusters, it is expelling its gas under the gentle pressure of stellar winds and the violent shocks of massive supernovae. Its stars are being swept by immense galactic tides that are slowly stretching the cluster out into a long stream.

Recently, as telescopes like Gaia and TESS have mapped out the millions of stars that lie around us, astronomers have started to look at how this process is playing out. Several clusters close to Earth, they have found, seem to have formed around a similar time and in a similar place, and are therefore probably linked to the Pleiades.

In blue are the original stars of the Pleiades, shown against the plane of the Milky Way. In yellow are the stars now thought to have formed together with it. NASA’s Goddard Space Flight Center; background, ESA/Gaia/DPAC; Boyle et. al. 2025

A new study has strengthened this idea. By looking at the properties, orbits, and probable ages of nearby stars, its authors have identified thousands that seem to have been born with the Pleiades. These sisters – and they number over three thousand – are now scattered across the night sky, and cover a region more than a thousand light-years across.

Many of these stars also show the chemical characteristics of the Pleiades. They are distinct in how much magnesium and silicon they contain, a fingerprint that comes from their parent cloud of gas and dust. Put together – orbits, ages, and chemicals – this all strongly suggests these stars emerged from the same place.

Astronomers have named this loose collection the Greater Pleiades Complex. It is slowly dissolving, and will continue to do so for tens of millions of years to come. Eventually it will be lost entirely, and the sisters of the Pleiades will be scattered forever across the hundreds of billions of stars in our galaxy.

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A Black Hole Superflare

Astronomers call them transients. Every now and then an object in the night sky suddenly brightens, shines strongly for a few days or weeks, and then fades away. Sometimes these are supernovae, giant stars exploding and releasing powerful bursts of energy in their final moments. At other times they are smaller novae, jets from unstable stars, or the result of violent collisions between stellar beings.

Back in 2018, one of these transients was picked up by an automated survey. Initial studies had found nothing particularly interesting about it. But in 2023, after noticing that the object had faded less slowly than expected, astronomers decided to take another look.

That revealed something surprising. The event had taken place at an enormous distance, and the responsible object lay at least ten billion light-years from Earth. For it to be visible from such a distance it must have been incredibly bright and that means it must have been something spectacular and violent.

Studies after 2023 showed the object was probably a black hole, and that the burst of light came from a star in its vicinity. The intense warping of a black hole can sometimes magnify light and make things seem brighter than they really are. But according to the authors of a recent study into the event, that doesn’t seem to be the case here.

Instead, they think the burst came from a star ripping apart as it approached the black hole. It was probably a massive star, one with at least thirty times the mass of the Sun. As it ventured towards the black hole powerful tides would have swept across it. Eventually they become too much for it to survive, and the star was torn apart in a “tidal disruption event”.

We have seen such events before, but this one was the most energetic ever spotted. That means it was probably the largest star we’ve ever witnessed falling into a black hole. Astronomers, of course, plan to keep watching it: as the event has not yet faded away, remnants of the giant star are probably still spinning around the black hole. Over the coming years they should slowly be consumed, and the transient – barring a few more outbursts – should finally fade away.

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Blue Origin Dreams Big

On November 13, Blue Origin sent a pair of spacecraft towards Mars. The duo, which together form a single mission known as Escapade, will study how the solar wind interacts with the weak magnetic field around the Red Planet.

For Blue Origin the launch was a triumph. It was only the second flight of the New Glenn rocket, and for the first time the company managed to steer the rocket’s booster back to a safe landing on a waiting barge. This now paves the way for Blue Origin to start reusing rockets, and thus provide a real competitor to SpaceX’s Falcon rocket.

The New Glenn booster stands on the recovery barge as it returns to shore. Credit: Blue Origin.

But Blue Origin is not stopping there. The next flight of New Glenn will target the Moon, and will carry the company’s first lunar lander. Blue Moon is designed to carry cargo to the lunar surface – that might be, for example, rovers, supplies for future missions, or other scientific experiments. If the company succeeds in putting it down safely, they will move on to testing a crewed version.

In this, too, Blue Origin is hoping to rival SpaceX. At the moment, NASA’s plans for the Moon rely on SpaceX’s Starship. But development of this enormous rocket is proceeding more slowly than hoped, and America’s politicians are starting to talk about finding an alternative.

Blue Origin is targeting a lunar landing for January 2026, and plan to follow that with a demonstration of the crewed version by 2027. If they succeed, SpaceX might well start to feel some pressure.

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A Stunning Solar Show

A series of solar flares erupted in mid-November. Each was powerful, and one of them – on November 12 – was among the strongest of the decade. Alongside these flares came coronal mass ejections, each a cloud of solar material sent hurtling out into space. As they hit the Earth, they created vivid auroras, some of which were visible as far south as Mexico.

The flares had some minor consequences on our technology. The European Space Agency warned of disruption to satellite navigation services. Radio communications were badly affected across Europe and Africa. The launch of Escapade to Mars was postponed by a day: NASA feared the spacecraft might be damaged by the passing storm.

The Sun is still near the peak of its eleven-year-long cycle of activity. The number of visible sunspots is often used to track this cycle, and that reached a peak only in August last year. Numbers are now falling, but remain high. Nevertheless, the Sun should calm down over the next few years.

From NOAA, the number of sunspots seen over the past decade. Numbers peaked in mid-2024, they are now falling. In pink are the projected numbers for the years ahead.

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