Tag: Stars

Why Is The Sky Dark At Night?

That question is not as simple as it may sound. You might think that space appears dark at night because that is when our side of Earth faces away from the Sun as our planet rotates on its axis every 24 hours.

But what about all those other far away suns that appear as stars in the night sky? Our own Milky Way galaxy contains over 200 billion stars, and the entire universe probably contains over 100 billion galaxies.

You might suppose that that many stars would light up the night like daytime!

Until the 20th century, astronomers didn’t think it was even possible to count all the stars in the universe. They thought the universe went on forever. In other words, they thought the universe was infinite.

Besides being very hard to imagine, the trouble with an infinite universe is that no matter where you look in the

night sky, you should see a star.

Stars should overlap each other in the sky like tree trunks in the middle of a very thick forest.

But, if this were the case, the sky would be blazing with light. This problem greatly troubled astronomers and became known as “Olbers’ Paradox.” A paradox is a statement that seems to disagree with itself.

To try to explain the paradox, some 19th century scientists thought that dust clouds between the stars must be absorbing a lot of the starlight so it wouldn’t shine through to us.




But later scientists realized that the dust itself would absorb so much energy from the starlight that eventually it would glow as hot and bright as the stars themselves.

Astronomers now realize that the universe is not infinite. A finite universe—that is, a universe of limited size—even one with trillions and trillions of stars, just wouldn’t have enough stars to light up all of space.

Although the idea of a finite universe explains why Earth’s sky is dark at night, other causes work to make it even darker.

Not only is the universe finite in size, it is also finite in age. That is, it had a beginning, just as you and I did.

The universe was born about 15 billion years ago in a fantastic explosion called the Big Bang. It began at a single point and has been expanding ever since.

Because the universe is still expanding, the distant stars and galaxies are getting farther away all the time. Although nothing travels faster than light, it still takes time for light to cross any distance.

So, when astronomers look at a galaxy a million light years away, they are seeing the galaxy as it looked a million years ago.

The light that leaves that galaxy today will have much farther to travel to our eyes than the light that left it a million years ago or even one year ago, because the distance between that galaxy and us constantly increases.

That means the amount of light energy reaching us from distant stars dwindles all the time. And the farther away the star, the less bright it will look to us.

The universe, both finite in size and finite in age, is full of wonderful sights.

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What Makes A Star A Star?

How do you separate a true star from the stellar wannabes of the Universe? After a decade of collecting data, astronomer Trent Dupuy thinks he finally has the answer.

With so many objects known to sit in that weird middle ground between giant planets and tiny stars, scientists have struggled to boil it down to a simple answer. What Dupuy boils it down to is mass.

Mass is the single most important property of stars because it dictates how their lives will proceed,” Dupuy, from the University of Texas at Austin, explained at the American Astronomical Society’s summer meeting earlier this month.

We benefit from that here on Earth, as our Sun is in the stellar goldilocks zone – its mass is just right to sustain nuclear fusion within its core for billions of years. This has provided the conditions for life to develop and evolve on our planet.

But not everything in the galaxy is so nice and stable. More massive stars burn through their nuclear fuel quicker, dye young, and go out with a violent bang in the form of a supernova.

Less massive objects, like brown dwarfs, are like stellar runts, possessing more mass than a planet, yet not enough mass to be a fully fledged star.

Often referred to as failed stars, they’re ubiquitous throughout the Universe, but their exceedingly dim glow makes these objects difficult to study.




First proposed to exist 50 years ago, these enigmatic objects help bridge the gap between stars and planets, but it wasn’t until more recently that astronomers began to study them in great detail.

Stars like the Sun shine as a result of nuclear reactions that constantly converts the supply of hydrogen in their cores into helium.

These same reactions determine how bright a star shines – the hotter the core, the more intense the reaction and subsequently the brighter the star’s surface will be. As expected, less massive stars are dimmer due to cooler centres, which produce slower reactions.

Don’t let the name fool you – brown dwarfs aren’t always brown. These stellar wannabes are actually red when they form, then turn to black as they slowly fizzle out over trillions of years.

That’s because despite outweighing even the largest of planets, brown dwarfs have so little mass that their centres aren’t hot enough to sustain nuclear reactions.

In the 1960s, astronomers theorised that there must be a mass limit for fusion.

Previous studies of stellar evolution have suggested that the boundary between red dwarfs (the smallest stars) and brown dwarfs was around 75 Jupiter masses (or roughly 7-8 percent of the Sun).

But until now, his measurement was never directly confirmed.

Dupuy and Michael Lui of the University of Hawaii spent the past 10 years studying 31 binary pairs of brown dwarfs with the help of the most powerful telescopes on Earth – the Keck Observatory and the Canada-France-Hawaii Telescope, as well as some input from Hubble.

By analysing a decade’s worth of imagery, Dupuy and Liu have created the first large sample study of brown dwarfs masses.

According to Dupuy, an object must weigh the equivalent of 70 Jupiters in order to spark nuclear fusion and become a star, which is slightly less than previously suggested.

The duo also determined there’s a temperature cut-off, with any object cooler than 1,600 Kelvin (approximately 1,315 Celsius and 2,400 degrees Fahrenheit) classified as a brown dwarf.

The study will help astronomers better understand the conditions under which stars form and evolve – or in the case of brown dwarfs, fail.

It could also provide new insight into planetary formation as the success or failure of star formation directly impacts the star systems they could potentially produce.

The research will be published in an upcoming edition of The Astrophysical Journal Supplement, and a pre-print is available here.

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Puzzling Cosmic Glow Is Caused by Diamond Dust Glamming Up Stars

Diamond dust is responsible for a mysterious glow emanating from certain regions of the Milky Way galaxy, a new study reports.

Astronomers have long known that some type of very small, rapidly spinning particle is throwing off this faint light, which is known as anomalous microwave emission (AME). But they couldn’t identify the exact culprit — until now.

In the new study, researchers used the Green Bank Telescope in West Virginia and the Australia Telescope Compact Array to search for AME light in 14 newborn star systems across the Milky Way.

They spotted the emissions in three of these systems, coming from the planet-forming disks of dust and gas swirling around the stars.

This is the first clear detection of anomalous microwave emission coming from protoplanetary disks,” study co-author David Frayer, an astronomer with the Green Bank Observatory, said in a statement.




The study team also detected the unique infrared-light signatures of nanodiamonds — carbon crystals far smaller than a grain of sand — in these same three systems, and nowhere else.

In fact, these [signatures] are so rare, no other young stars have the confirmed infrared imprint,” study lead author Jane Greaves, an astronomer at Cardiff University in Wales, said in the same statement.

The researchers don’t think this is a coincidence.

One to 2 percent of the total carbon in these protoplanetary disks has been incorporated into nanodiamonds, according to the team’s estimates.

Another leading AME-source candidate, a family of organic molecules known as polycyclic aromatic hydrocarbons (PAHs), doesn’t hold up under scrutiny, the researchers said.

The infrared signature of PAHs has been identified in multiple young star systems that lack an AME glow, they noted.

The new results could help astronomers better understand the universe’s early days, study team members said.

Scientists think the universe expanded far faster than the speed of light shortly after the Big Bang, in a brief period of “cosmic inflation.

If this did indeed happen, it should have left a potentially detectable imprint — an odd polarization of the cosmic microwave background, the ancient light left over from the Big Bang.

The new study provides “good news for those who study polarization of the cosmic microwave background, since the signal from spinning nanodiamonds would be weakly polarized at best,” said co-author Brian Mason, an astronomer at the National Radio Astronomy Observatory in Charlottesville, Virgina.

This means that astronomers can now make better models of the foreground microwave light from our galaxy, which must be removed to study the distant afterglow of the Big Bang,” Mason added.

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Gaia Mission Releases Map Of More Than A Billion Stars – Here’s What It Can Teach Us

Most of us have looked up at the night sky and wondered how far away the stars are or in what direction they are moving.

The truth is, scientists don’t know the exact positions or velocities of the vast majority of the stars in the Milky Way.

But now a new tranche of data from the European Space Agency’s Gaia satellite, aiming to map stars in our galaxy in unprecedented detail, has come in to shed light on the issue.

The Gaia Archive opened on April 25, making public Gaia’s second data release to everyone.

To quote the character Dave Bowman in the sci-fi classic 2001: A Space Odyssey: “It’s full of stars”. In fact, it contains data on the distances to more than 1.3 billion stars.

The Gaia satellite was launched in 2013 and has been scanning the sky with its two telescopes continuously ever since, with the aim of deciphering how our Milky Way galaxy formed and evolved.




To do this, it is measuring something called parallax. If you hold a finger at arms length and look at it with one eye and then the other, your finger appears to shift position compared to the background.

The angular change is called parallax.

Being in space allows Gaia to see similar tiny shifts in star positions. Observations at different locations six months apart (half way of its orbit around the Earth) are akin to looking at your finger with one eye and then the other.

When you know the parallax as well as the distance from Gaia to the sun (or the distance from your nose to your eye), you can use simple trigonometry to work out the distance to each star (or your finger).

Gaia also sees stars move in the plane of the sky over time. These units of “angle per time” can be converted to a physical unit of speed (for example kilometres per second) if we know the distance to the stars.

However, to know how a star is moving in three dimensions in space requires that we also measure the speed perpendicular to the sky along the line-of-sight. This requires a galactic speed camera!

A normal radar speed camera uses the Doppler effect – the stretching or squashing of waves because of motion – by measuring the change in the radio frequency from signals bounced off cars to measure their speed.

Similarly, Gaia measures the change in frequency in the light from stars to check their speed. The star light is bluer if the star is moving towards us or redder if the star is moving away from us. This is called radial velocity.

Gaia’s first data release in 2016 published the distances of around two million stars but did not include any radial velocities.

However we already knew the radial velocity of less than 400,000 of these stars – measured from the ground by many different surveys.

Gaia’s second data release includes information on sky positions and brightness for nearly 1.7 billion stars and more than seven million radial velocities.

Not only does this make Gaia the largest radial velocity survey ever – it increases the number of stars with accurate 3D space velocities by a factor of 18.

A series of Gaia science demonstration papers have also been published alongside the star catalogue. I was involved in the research behind one of these papers, constructing the most detailed map ever of 3D space velocities to date.

The next data release by Gaia will be in 2020. This is expected to boost the numbers of stars with known radial velocities from seven million today to around 30m – keeping our team busy for several years yet.

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TRAPPIST-1 Planets Probably Rich In Water

Planets around the faint red star TRAPPIST-1, just 40 light-years from Earth, were first detected by the TRAPPIST-South telescope at ESO’s La Silla Observatory in 2016.

In the following year further observations from ground-based telescopes, including ESO’s Very Large Telescope and NASA’s Spitzer Space Telescope, revealed that there were no fewer than seven planets in the system, each roughly the same size as the Earth.

They are named TRAPPIST-1b,c,d,e,f,g and h, with increasing distance from the central star.

Further observations have now been made, both from telescopes on the ground, including the nearly-complete SPECULOOS facility at ESO’s Paranal Observatory, and from NASA’s Spitzer Space Telescope and the Kepler Space Telescope.

A team of scientists led by Simon Grimm at the University of Bern in Switzerland have now applied very complex computer modelling methods to all the available data and have determined the planets’ densities with much better precision than was possible before.




Simon Grimm explains how the masses are found: “The TRAPPIST-1 planets are so close together that they interfere with each other gravitationally, so the times when they pass in front of the star shift slightly.

“These shifts depend on the planets’ masses, their distances and other orbital parameters. With a computer model, we simulate the planets’ orbits until the calculated transits agree with the observed values, and hence derive the planetary masses.”

Team member Eric Agol comments on the significance: “A goal of exoplanet studies for some time has been to probe the composition of planets that are Earth-like in size and temperature.

“The discovery of TRAPPIST-1 and the capabilities of ESO’s facilities in Chile and the NASA Spitzer Space Telescope in orbit have made this possible — giving us our first glimpse of what Earth-sized exoplanets are made of!

The measurements of the densities, when combined with models of the planets’ compositions, strongly suggest that the seven TRAPPIST-1 planets are not barren rocky worlds.

They seem to contain significant amounts of volatile material, probably water, amounting to up to 5% the planet’s mass in some cases — a huge amount; by comparison the Earth has only about 0.02% water by mass!

TRAPPIST-1b and c, the innermost planets, are likely to have rocky cores and be surrounded by atmospheres much thicker than Earth’s.

TRAPPIST-1d, meanwhile, is the lightest of the planets at about 30 percent the mass of Earth. Scientists are uncertain whether it has a large atmosphere, an ocean or an ice layer.

Scientists were surprised that TRAPPIST-1e is the only planet in the system slightly denser than Earth, suggesting that it may have a denser iron core and that it does not necessarily have a thick atmosphere, ocean or ice layer.

It is mysterious that TRAPPIST-1e appears to be so much rockier in its composition than the rest of the planets.

In terms of size, density and the amount of radiation it receives from its star, this is the planet that is most similar to Earth.

TRAPPIST-1f, g and h are far enough from the host star that water could be frozen into ice across their surfaces.

If they have thin atmospheres, they would be unlikely to contain the heavy molecules that we find on Earth, such as carbon dioxide.

Astronomers are also working hard to search for further planets around faint red stars like TRAPPIST-1. As team member Michaël Gillon explains: “This result highlights the huge interest of exploring nearby ultracool dwarf stars — like TRAPPIST-1 — for transiting terrestrial planets.

“This is exactly the goal of SPECULOOS, our new exoplanet search that is about to start operations at ESO’s Paranal Observatory in Chile.

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Astronomers Found Evidence For A ‘Dark’ Gravitational Force That Might Fix Einstein’s Most Famous Theory

Albert Einstein’s general theory of relativity predicts so much about the universe at large, including the existence of gravitational lenses or “Einstein rings.”

And yet his famous equations struggle to fully explain such objects.

While general relativity says a strong source of gravity — like the sun— will warp the fabric of space, bend light from a distant object, and magnify it to an observer, very big objects like galaxies and galaxy clusters make gravitational lenses that are theoretically too strong.




General relativity also can’t fully explain the spinning motions of galaxies and their stars.

That’s why most physicists think as much as 80% of the mass in the universe is dark matter: invisible mass that hangs out at the edges of galaxies.

Dark matter might be made of hard-to-detect particles, or perhaps an unfathomable number of tiny black holes. But we have yet to find smoking-gun evidence of either.

However, a contentious theory by Erik Verlinde at the University of Amsterdam suggests dark matter may not be matter at all.

What’s more, astronomers say his idea “is remarkable” in its ability to explain the behavior of more than 33,000 galaxies that they studied.

This does not mean we can completely exclude dark matter, because there are still many observations that Verlinde’s theory cannot yet explain,” study leader and physicist Margot Brouwer said in a YouTube video about the research.

However it is a very exciting and promising first step.”

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Here’s How To Send Your Name Hurtling Into The Sun This Year

If you’ve ever wanted to send a part of you hurtling into the Sun, this is your lucky day. NASA is offering you the chance to send your name rocketing towards our favorite ball of gas aboard the Parker Solar Probe.

The $1.5-billion mission will be the first-ever probe to “touch” the Sun, traveling directly into its atmosphere later this year.

The mission will go seven times closer to the Sun than any other man-made object, in order to study its atmosphere.

It’ll go hurtling towards the center of our solar system at speeds of 700,000 kilometers per hour. “That’s fast enough to get from Philadelphia to Washington, DC, in one second,” NASA wrote.




Your name, if you fancy it, will be included on a memory card within the probe’s payload, traveling at speeds previously unknown to any of your nametags.

The mission will study how energy and heat move through the solar corona. By studying the Sun – the only star available for us to study up close – scientists also hope to learn more about stars throughout the Universe.

The probe will seek to discover what accelerates solar wind and solar energetic particles, which NASA says it has sought answers to for over 60 years.

Now with thermal engineering advances, NASA is finally able to send a probe that can withstand the immense heat.

At its closest approach, the probe will face temperatures of 1,370°C (2,500°F), but the probe’s solar shields will astonishingly keep the payload at around room temperature.

So your name will stay cool, don’t worry. Unless it’s something like “Nigel”, which has never been cool in the first place.

The initiative of sending your name along for the ride, dubbed “Hot Ticket“, was launched this week by Star Trek actor and musical legend William Shatner.

The first-ever spacecraft to the Sun, NASA’s Parker Solar Probe, will launch this year on a course to orbit through the heat of our star’s corona, where temperatures are greater than 1 million degrees,” Shatner said in a video launching the project.

The spacecraft will also carry my name to the Sun, and your name, and the names of everyone who wants to join this voyage of extreme exploration.

In order to get your name aboard the probe, it really is as simple as applying. Just go to NASA’s Parker Solar Probe website and enter your details before April 27, 2018.

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Universe’s First Stars Detected? Here Are The Facts!

Stars are our constant companions in the night sky, but seas of twinkling lights weren’t always a feature of the cosmos.

Now, scientists peering back into deep time suggest that the earliest stars didn’t turn on until about 180 million years after the big bang, when the universe as we know it exploded into existence.

For decades, teams of scientists have been chasing—in fact, racing—to detect the signatures of these first stars.

The new detection, from a project called EDGES, is in the form of a radio signal triggered when light from those stars began interacting with the hydrogen gas that filled primordial empty space.

If the signal stands up to scrutiny, the detection simultaneously opens up a new line of cosmological inquiry and offers a few conundrums to tackle.

The era of cosmic dawn has been entirely uncharted territory until now,” says physicist Cynthia Chiang of the University of KwaZulu-Natal in South Africa.

It’s extremely exciting to see a new glimpse of this slice of the universe’s history, and the EDGES detection is the initial step toward understanding the nature of the first stars in more detail.




Cosmic Dawn

Shortly after the universe was born, it was plunged into darkness. The first stars turned on when hot gas coalesced around clumps of dark matter, then contracted and became dense enough to ignite the nuclear hearts of infant suns.

As those early stars began breathing ultraviolet light into the cosmos, their photons mingled with primordial hydrogen gas, causing it to absorb background radiation and become translucent.

When that happened, those hydrogen atoms produced radio waves that traveled through space at a predictable frequency, which astronomers can still observe today with radio telescopes.

The same process is going on in modern stars as they continue to send light into the cosmos.

But the radio waves produced by those first stellar gasps have been traveling through space for so long that they’ve been stretched, or redshifted.

That’s how astronomers identified the fingerprints of the earliest stars in radio waves detected by a small antenna in western Australia.

From Light to Dark

If the signal is real, it presents a challenge for some scientists who’ve been thinking about how the early universe worked.

For starters, the time frame during which these earliest stars emerged lines up well with some theories, but it’s not exactly bang on with others.

In previous work, Furlanetto and his colleagues started with actual observations of the earliest known galaxies, and then rewound the cosmic clock using computer models, searching for the age at which a signal from the first stars might appear.

The universe’s first galaxies are thought to be small, fragile, and not that great at birthing stars, so Furlanetto wouldn’t expect the signal to peak until about 325 million years after the big bang.

But if the first stars had already furnished enough light to make their presence known 180 million years after the big bang, those early galaxies must be doing something different.

As well, the primordial hydrogen gas is absorbing photons at rates that are at least two times higher than predicted.

That’s problematic for some ideas about the temperature of the early universe. It means that either the primordial gas was colder than expected, or background radiation was hotter.

Dark matter makes up the bulk of the universe’s mass, but it doesn’t behave like normal matter and has proven tricky to understand.

It regularly evades direct detection, and scientists are struggling to pin down, what, exactly it is and how it has influenced the structure of the universe through time.

But, she notes, it’s way too early to accept that conclusion.

An alternate possibility is that there are simply more photons for the hydrogen gas to absorb, though it’s not obvious where all those photons would come from in the early universe.

So she and others are waiting for independent confirmation of the EDGES result before diving too deep into the possible dark matter scenarios.

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Unprecedented Image Of A Supernova 80 Million Light Years Away Is Captured For The First Time By An Amateur Astronomer

The first burst of light given off by an exploding star has been captured for the first time by an amateur astronomer in Argentina.

Observations of a dying star 80 million light-years away, taken by Víctor Buso, 60, has given scientists their first view of the initial flash given off by a supernova.

To date, no one has been able to capture the ‘first optical light’ from a supernova, since stars explode seemingly at random in the sky, and the burst is fleeting.

Most are only spotted a long time after the initial blast, making Mr Buso’s one-in-ten-million observations ‘unprecedented‘, scientists said.

The new data provide important clues to the physical structure of the star just before its catastrophic demise and to the nature of the explosion itself.

Professional astronomers have long been searching for such an event,” said University of California at Berkeley astronomer Dr Alex Filippenko, who followed up the lucky discovery with scientific observations of the explosion, called SN 2016gkg.




Observations of stars in the first moments they begin exploding provide information that cannot be directly obtained in any other way.”

It’s like winning the cosmic lottery.”

During tests of a new camera, Mr. Buso snapped images through his 16-inch telescope of the galaxy NGC 613, which is 80 million light-years from Earth.

He took a series of short-exposure photographs of the spiral galaxy, accidentally capturing it before and after the supernova’s ‘shock breakout’.

This is when a pressure wave from the star’s exploding core hits and heats gas at the star’s surface to a very high temperature, causing it to flash and rapidly brighten.

Upon examining the images, Mr. Buso, of Rosario, Argentina, noticed a faint point of light quickly brightening near the end of a spiral arm that was visible in his second set of images but not his first.

Astronomer Dr Melina Bersten and her colleagues at the Instituto de Astrofísica de La Plata in Argentina soon learned of the serendipitous discovery.

They realized that Mr. Buso had caught a rare event; part of the first hour after light emerges from a massive exploding star.

She estimated Mr Buso’s chances of such a discovery, his first supernova, at one in 10 million or perhaps even as low as one in 100 million.

Dr Bersten contacted an international group of astronomers to help conduct additional frequent observations of SN 2016gkg.

A series of subsequent studies have revealed more about the type of star that exploded and the nature of the explosion.

Mr. Buso’s discovery, snapped in September 2016, and results of follow-up observations have now been published in the journal Nature.

Buso’s data are exceptional,” Dr. Filippenko added.

This is an outstanding example of a partnership between amateur and professional astronomers.

The astronomer and his colleagues obtained a series of seven spectra, where the light is broken up into its component colors, as in a rainbow.

They used the Shane 3-meter telescope at the University of California’s Lick Observatory near San Jose, California, and the twin 10-meter telescopes of the W. M. Keck Observatory on Maunakea, Hawaii.

This allowed the international team to determine that the explosion was a Type IIb supernova: The explosion of a massive star that had previously lost most of its hydrogen envelope.

Combining the data with theoretical models, the team estimated that the initial mass of the star was about 20 times the mass of our Sun.

They suggest it lost most of its mass to a companion star and slimmed down to about five solar masses prior to exploding.

Further analyses of the signal could provide further information on the star’s structure and uncover more secrets about supernovas.

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There Might Be More Big Stars In The Universe Than We Thought

A new series of observations suggests that we have underestimated the number of large stars that form in starburst events. If this finding is more than just an exception to the rule, there could be consequences for many astronomical theories.

As reported in Science, an international group of astronomers has studied the stars within 30 Doradus, also known as the Tarantula Nebula, a starburst region in the Large Magellanic Cloud.

The team managed to characterize the properties of 452 stars in 30 Doradus and, out of all of them, 247 were more massive than 15 times our Sun.




There are about 25 to 50 more heavy stars than theoretical predictions, known as the initial mass function (IMF), would expect.

The IMF describes the distribution of masses for any population of stars when it formed. It’s an empirical distribution and is very important. The mass of stars determines their evolution and how they’re going to end their life.

For example, more massive stars mean more supernovae, which leads to more black holes and neutron stars. It also influences the evolution of the stars’ host galaxies as a whole.

And since galaxies have up to 100 billion stars, the IMF is very useful for providing statistics.

Nevertheless, this doesn’t mean that the IMF is perfect. Since its proposal in 1955 by Edwin Salpeter, the IMF has been tweaked to better characterize the low-mass end of star mass distribution.

It turns out that there are a lot more small stars than predicted, and the new study suggests that some tweaking might be necessary for certain environments, even at the high end of mass distribution.

The study raises several questions that will require more observation. Is the excess of massive stars connected to advantageous conditions in the gas clouds?

Is it common during starburst events? Are there other mechanisms at work?

What remains interesting is the presence of some of the most massive stars ever observed, with some weighing over 200 times the mass of the Sun.

The researchers estimate that bigger stars might still exist in the core of the nebular, which was not resolved.

The Tarantula Nebula is the most active and largest (over 600 light-years) starburst region in the local group of galaxies.

Supernova 1987A, the closest supernova observed since the invention of the telescope, occurred on the outskirts of this nebula.

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