Last Updated on June 13, 2026 by Staff
Astronomers have made a step forward in understanding a really mysterious X-ray event that happened in a globular cluster. They used the Chandra X-ray Observatory to look at a flare that was found in the globular cluster NGC 6540 almost twenty years ago. The Chandra Telescope found some new things about this flare.
The globular cluster NGC 6540 is 12,000 light-years away from Earth in the Milky Way galaxy. Globular clusters are groups of stars that are held together by gravity. These groups of stars are like laboratories where astronomers can study how stars and galaxies change over time.
Astronomers are really interested in NGC 6540 because they found some X-ray sources in the cluster. One of these sources had a powerful flare that nobody can explain.
The Weird X-Ray Flash
This mysterious object is called 3XMM J180608.9–274553 or J1806 for short. It was first seen in September 2005 when the European Space Agency’s XMM-Newton satellite was looking at it. The source had a strong X-ray flare that only lasted for about 300 seconds.
What was really strange about this event was how brighter the source became. During the flare it was 100 times brighter than normal and then it quickly got faint again. This kind of thing is really rare and hard to explain.
For a time astronomers were trying to figure out what could have caused the flare. Some people thought it might be because of a binary star system while others thought it could be something unusual like a black hole.
To solve the mystery, astronomers started a study using the Chandra X-ray Observatory.
What the Chandra Telescope Found
The new study was led by Andrea Sacchi from the Institute of Space Astrophysics and Cosmic Physics in Italy. They used the Chandra Telescope to look closely at the area where J1806 was found. They also used some data from XMM-Newton.
One of the discoveries they made was that what they thought was one X-ray source was actually three separate sources. The Chandra Telescope has good instruments that can see things that are really close together.
These new sources were called Source A, Source B and Source C. They are really close to each other which makes them hard to tell apart.
The astronomers also found six X-ray sources near the center of the cluster. This shows that the area is really complicated and crowded.
The Mystery Is Not Solved
Even though they found these new sources the mystery of the flare is still not solved.
The astronomers looked at a few ideas to explain the flare. One idea was that it could have been caused by a binary star system where one star makes the other star look brighter.. When they did the math it did not seem like it would work.
They also thought about the possibility of a mass black hole. These black holes are bigger than the ones that form from stars. Smaller than the ones at the centers of galaxies.
This idea did not work either. The flare was not coming from the center of the cluster, where a black hole would usually be. The flare did not last as long as it would if it was coming from a black hole.
So the Chandra Telescope did not figure out what is causing the flare.
What Happens Next
Even though the mystery is still not solved, the study is a step forward in understanding the X-ray sources in NGC 6540.
Now that they have separated the sources astronomers have a better idea of what is going on in the cluster. The findings will help guide studies and theories.
Astronomers hope that they can use the Chandra Telescope and other telescopes in the future to learn more about the flare. If they can understand things like this they might discover types of objects in space or learn about new physical processes that happen in really dense groups of stars.
For now J1806 is still one of the unsolved puzzles in astronomy. The Chandra Telescope has given us some clues. The source of the flare is still a mystery that astronomers want to solve.