Star clusters give birth like dogs, not humans, ALMA shows | by Ethan Siegel | Starts With A Bang! | Jan, 2024

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This false-color look inside the star-forming region G333.23–0.06 shows ALMA data of multiple systems of high-mass protostars. Within these clumps of matter, ALMA has found multi-star systems, with singlet stars being a relative rarity. (Credit: S. Li, MPIA / J. Neidel, MPIA Graphics Department; Data: ALMA Observatory)

Here in our Solar System, we only have one star: a singlet. For many systems, including the highest-mass ones, that’s anything but the norm.

Humanity once thought our Solar System was typical.

Here in our own Solar System, a single star anchors the system, where inner, rocky planets, an intermediate-distance asteroid belt, and then more distant gas giant planets eventually give way to the Kuiper belt and Oort cloud. For a long time, we assumed this configuration was typical and common. Today, we know better. (Credit: NASA/Dana Berry)

The other stars, presumably, were Sun-like objects, but very far away.

The brightness distance relationship, and how the flux from a light source falls off as one over the distance squared. The earliest estimates for the distances to the stars assumed they were intrinsically as bright as the Sun, and that their faint appearance was solely caused by their great distance from us. (Credit: E. Siegel/Beyond the Galaxy)

We soon learned that stars and stellar systems varied tremendously.

The (modern) Morgan–Keenan spectral classification system, with the temperature range of each star class shown above it, in kelvin. In terms of size, the smallest M-class stars are still about 12% the diameter of the Sun, but the largest main sequence stars can be dozens of times the Sun’s size, with evolved red supergiants (not shown) reaching hundreds or even 1000+ times the size of the Sun. A star’s (main sequence) lifetime, color, temperature, and luminosity are all primarily determined by a single property: mass. (Credit: LucasVB/Wikimedia Commons; Annotations: E. Siegel)

Individual stars come in many different masses, temperatures, and colors.

Binary systems typically have unequal masses, unequal brightnesses, and orbit a barycenter that lies outside of both stars. Only if the alignment with respect to us is sufficiently edge-on, at right, will it appear as an eclipsing binary. Wide binaries, with separations of thousands of astronomical units (AUs), are exceptionally difficult to characterize. Approximately 35% of all stars are found in binary systems, with half in singlet systems and the remainder in trinary or even richer multi-star systems. (Credit: Zhatt and Stanlekub/Wikimedia Commons)

While our Solar System has just one star, half of all stellar systems have multiples.

The richest star system among the more familiar stars is Castor: the 24th brightest star in the sky and an intrinsically sextuple system. Unlike our Sun, which is the only star in our system, practically half of all stars have one or more companions in their stellar systems. (Credit: NASA)

Surveying nearby stars reveals that 48% of them are bound in multi-star systems.

The central concentration of this young star cluster found in the heart of the Tarantula Nebula is known as R136, and contains many of the most massive stars known. Among them is R136a1, which comes in at about ~260 solar masses and shines brighter than more than 8 million suns, making it the heaviest known star. Although great numbers of cooler, redder stars are also present, the brightest, bluest ones dominate this image, although they have the shortest lifetime, living for between 1–10 million years only. Finding populations of nearby, dust-free massive stars is an exceedingly challenging task; R136 is over 165,000 light-years away. (Credit: NASA, ESA, CSA, STScI, Webb ERO Production Team)

But what about the heaviest, most massive stars of all?

This fragment of the young star-forming region NGC 2014 showcases many stars that are bluer, more massive, and much shorter lived than our Sun. However, the fainter, redder, less luminous stars are far more numerous, making us wonder just what “typical” truly is for a star. NGC 2014 is also found in the Large Magellanic Cloud: over 160,000 light-years away. (Credit: NASA, ESA and STScI)

They’re too short-lived to perform an accurate census of them.

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