Ringed object holds the answers to the mystery of the missing star

Astronomers have cracked the case of a massive star that strangely went missing for nine months.

At twice the size of our sun, ASASSN-24fw became quite a mystery when it started to dim towards the end of 2024. While stars do often dim, they usually brighten again after a few days or weeks.

However, this super-sized star stayed dark for nine months, dimming to just 3 per cent of its usual observed brightness and making it very difficult for astronomers to see it.

The team studying the star believed the dimming was caused by another object passing in front of it – most likely a brown dwarf*, or a super-Jupiter* planet. Both are large “objects” that are smaller than stars but bigger than most planets.

Brown dwarfs are generally about 13 to 80 times the mass of Jupiter.

Jupiter is the largest planet in our solar system, about 11 times the size of Earth.

Meanwhile, super-Jupiter planets are even bigger.

Losing something that gigantic was no small blip on the screen.

The ring system shifting in front of the star was thought to block about 97 per cent of ASASSN-24fw’s light, causing the dimness.

It took nine months for the shifting to allow for the star’s brightness to shine through once more, but by then, it was in the constellation* Monoceros*, which was 3200 light-years away in space.

Its unexpected reappearance has given researchers immeasurable* insight into that corner of the universe.

“Long-lasting dimming events like this are exceptionally uncommon, as they require very perfect line-ups,” said Sarang Shah, lead author at India’s Inter-University Centre for Astronomy and Astrophysics*.

“The dimming began gradually because the outer parts of the rings are thin, and only became obvious when the denser regions passed in front of the star,” he said.

Rings were also “very difficult to observe directly to determine their characteristics,” said co-author Dr Jonathan Marshall, who is affiliated with Academia Sinica in Taiwan.

The rings’ lack of clear visibility was despite the fact that they’re “expected around massive objects”, he said.

Once ASASSN-24fw was back in full brightness, astronomers were able to figure out its mass and motion — leading them to estimate that it weighs more than three times as much as Jupiter.

The research team now plans to measure the star’s temperature, makeup, age and life stage.

They suggested it would realign with the ringed object again in about 42 years, which would present another opportunity to study the mysterious phenomenon once more.

POLL

GLOSSARY

• brown dwarf: celestial bodies that are bigger than planets yet not quite as big as stars. According to NASA, brown dwarfs form in the same way as main sequence stars except that they never gain enough mass to do fusion, a nuclear process that creates huge amounts of energy as light and heat. Brown dwarfs emit almost no light and are not visible to the naked eye or backyard telescopes
• super-Jupiter: a giant gas exoplanet that has a much larger mass than Jupiter
• constellation: a globally recognised group of stars that forms a pattern in the night sky, usually named after an animal, shape or mythological figure
• Monoceros: ‘the unicorn’, a constellation on the celestial equator visible in both hemispheres between November and May
• immeasurable: so great it can’t be measured
• Astrophysics: the application of physics to the study of astronomy

EXTRA READING
Earth’s problem with space junk
Astronauts journey to next frontier
Have we found a second Earth?

QUICK QUIZ
1. How long did the star ASASSN-24fw go dim for?
2. What caused the star to dim to just 3 per cent of its usual observed brightness?
3. What is a super-Jupiter planet?
4. How big is Jupiter compared to Earth?
5. Which constellation was the star in once its brightness returned to normal?

LISTEN TO THIS STORY

CLASSROOM ACTIVITIES
1. Missing star
After reading the Kids News article, draw and label a diagram showing what you think passed in front of the star and caused it to dim.

Use the information from the article to help explain or add your own ideas and scientific reasoning.

Time: allow 15 minutes to complete this activity
Curriculum Links: Science, Personal and Social, Critical and Creative Thinking

2. Extension
Scientists suggested they could study this phenomenon again in 42 years. How old will you be then? What other scientific advances might have been made in 2068?!

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Time: allow 10 minutes to complete this activity
Curriculum Links: English, Science, Personal and Social, Critical and Creative Thinking

VCOP ACTIVITY
Wow word recycle
There are plenty of wow words (ambitious pieces of vocabulary) being used in the article. Some are in the glossary, but there might be extra ones from the article that you think are exceptional as well.

Identify all the words in the article that you think are not common words, and particularly good choices for the writer to have chosen.

Select three words you have highlighted to recycle into your own sentences.

If any of the words you identified are not in the glossary, write up your own glossary for them.

Extension
Find a bland sentence from the article to up-level. Can you add more detail and description? Can you replace any base words with more specific synonyms?

Down-level for a younger audience. Find a sentence in the article that is high level. Now rewrite it for a younger audience so they can understand the words without using the glossary.