Read our interview with Chris Lintott on the importance of citizen science in astronomy<\/a><\/strong><\/em><\/li> <\/ul> <\/div>

Credit: BBC\/The Sky at Night <\/figcaption> <\/figure> <\/div> <\/div>
Green Pea galaxies explained<\/strong><\/h2>
These systems attract attention because of their distinctive green colour, caused by bright emission from oxygen that is associated with star formation.<\/p>
They are dwarf galaxies, but they are forming stars at a rate that would be unusual in systems 10 times their size.<\/p>
They are the most efficient factories of stars in the local Universe, though no one can agree why.<\/p>
$\"The$
The hunt for Green Pea galaxies has been swept along by citizen scientists. The distinctive colour is due to the glow of excited oxygen. Credit: Richard Nowell and the Sloan Digital Sky Survey <\/figcaption> <\/figure>
Astronomers peering at the Green Peas with orbiting X-ray telescopes have found them much brighter than expected.<\/p>
Signs, perhaps, that black holes more massive than we would have ever expected in such dwarf galaxies are present.<\/p>
As if that wasn\u2019t intriguing enough, recent observations with the James Webb Space Telescope of high-redshift<\/a> galaxies in the early Universe look rather like our local Green Peas, suggesting that the latter might just be stragglers, the last systems to go through a spectacular stage that most galaxies got over billions of years ago.<\/p>
So studying the Peas is important, but there\u2019s a catch.<\/p>
$\"Blueberry$
Blueberry galaxies are thought to be faint, local relations of Green Peas, vigorously star-forming dwarf galaxies that dominated the early Universe. Credit: SDSS\/Huan Yang <\/figcaption> <\/figure>
What makes Blueberry galaxies blue<\/strong><\/h2> Though nowhere near as distant as the galaxies studied by the James Webb Space Telescope, Green Pea galaxies aren\u2019t that local, existing between about 2.5 and 4 billion lightyears<\/a> away.<\/p>
At those distances, the redshift caused by the expansion of the Universe shifts the oxygen emission towards the red, producing the distinctive green colour that allowed the Peas to be identified in the first place.<\/p>
Those hunting similar systems closer to home need to look for round, blue galaxies \u2013 which they\u2019ve started calling Blueberries.\u00a0<\/p>
Several punnets-worth of these systems are now known, and there is a science paper that takes a first look at their X-ray emission using ESA\u2019s XMM-Newton orbiting observatory.<\/p>
This is the first time any Blueberry galaxies have been observed at X-ray wavelengths, and the results are surprising.<\/p>
$\"An$
An artist’s impression of XMM-Newton. Credit: ESA-C. Carrie <\/figcaption> <\/figure>
Blueberry quandry<\/strong><\/h2>
While Green Peas seem bright at these wavelengths, most of the seven systems were less luminous in the X-ray than we\u2019d expect for galaxies of their size; all but two weren\u2019t even detected!<\/p>
So what\u2019s going on?<\/p>
One possibility is that the population of Blueberry galaxies may be very young, so much so that their stellar population hasn\u2019t yet evolved enough to produce binary systems with a normal star paired with a neutron star or black hole, which shine brightly in X-ray.<\/p>
If that\u2019s right, these small galaxies formed most of their stars in the last five million years, a blink of a cosmic eye.<\/p>
Confusingly, one of the systems (which Star Wars<\/em> fans will be pleased to hear is called BB8) glows surprisingly brightly.<\/p>
The researchers suggest this might host a growing black hole, but then we need to explain why only one of the systems does.<\/p>
With more mysteries found by these observations than solved, telescopes will be picking Blueberry galaxies for a long while yet.<\/p>
Chris Lintott was reading <\/em>X-ray Observations of Blueberry Galaxies by B Adamcov\u00e1 et al. Read it online at: arxiv.org\/abs\/2408.13572<\/a>.<\/em><\/strong><\/p>
This article appeared in the November 2024 issue of BBC Sky at Night Magazine<\/em><\/strong><\/p> <\/body><\/html>\n
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