Stars are formed inside massive clouds of gas and dust called molecular clouds. The nebulous hypothesis explains how it works. According to that hypothesis, dense nuclei inside these clouds of hydrogen collapse due to instability and form stars. The nebulous hypothesis is much more detailed than the short version, but that is the basic idea.
The problem is that it only explains how individual stars are formed. But about half of the Milky Way’s stars are binary pairs or more stars. The nebula hypothesis does not clearly explain how these stars are formed.
Most stars with about the same mass as our sun or larger are not single stars. Most are members of several star systems, especially binary stars. While nebula theory explains how single stars are formed, there are competing theories about how multiple stars are formed.
Remove all ads on Universe Today
Join our Patreon for as little as $ 3!
Get the ad-free experience of a lifetime
First of all, after a molecular cloud collapses into a star, it forms a rotating disk of gas and dust around the young protostar, which is called a circumferential disk. A theory that explains how multiple stars are formed says that a pair or more young protostars are fragments of a mother disk that was once much larger. Another theory states that the young protostars form independently, then capture each other in an orbital arrangement.
But when stars form inside a molecular cloud, it begins with a dense nucleus inside the cloud. This nucleus initiates the gravitational collapse that collects enough gas in one place to form a star. The question is what is different with some of these nuclei that cause more stars to form compared to single stars?
That’s what astronomers at Hawaiis do The James Clerk Maxwell Telescope (JCMT) wanted to understand.
JCMT is a 15-meter radio telescope at the Mauna Kea Observatory in Hawaii. The telescope’s submillimeter observations allow it to observe the molecular clouds where the stars are born. The researchers used it to observe Orion Molecular Cloud Complex (OMCC), the closest active star chamber to Earth, which is still about 1,500 light-years away. The OMCC contains two giant molecular clouds (GMCs), Orion A and Orion B. They also used observations from ALMA and Japan The Nobeyama telescope.
The team saw several star systems form in the Orion complex and made important discoveries about the process. They presented their results in an article published in The Astrophysical Journal. The magazine is “ALMA Survey of Orion Planck Galactic Cold Clumps (ALMASOP): How do dense core properties affect the diversity of protostars?The first author is Qiuyi Luo, a Ph.D. student at Shanghai Astronomical Observatory.
“During the transition phase from a prestellar to a protostellar cloud core, one or more protostars may form within a single gas core,” the paper writes. “However, the detailed physical processes for this transition are still unclear.”
For this study, the research team collected observations of 43 protostellar nuclei in Orion’s molecular cloud complex with JCMT. Then they used the powerful ALMA telescope to study the internal structure of the nuclei.
Research shows that about 30% of the 43 dense nuclei form binary or multiple stars, and the rest form only single stars. Astronomers measured and estimated the sizes and masses of the nuclei. They found that binary / multiple cores have higher densities and masses, although the sizes of all cores are not very different.
“This is understandable,” said lead author Qiuyi Luo. “Denser nuclei are much easier to fragment due to disturbances caused by self-gravity inside molecular nuclei.”
From there, the team turned to Japan’s 45-meter Nobayama radio telescope. They observed what is known as the N2H + J = 1-0 molecular line in all 43 dense nuclei. N2H + is diazenylium, one of the first ions ever found in interstellar clouds. This molecular line is easily observed through the Earth’s atmosphere with fine precision. Astronomers use it to map the density and velocity of gas in molecular clouds.
These observations showed that dense nuclei forming multiple stars are more turbulent than nuclei forming single stars.
“These Nobeyama observations provide a good measure of turbulence levels in dense nuclei. Our findings suggest that binary / multiple stars tend to form in more turbulent nuclei,” said Professor Ken’ichi Tatematsu, who led the Nobeyama observations.
Lead author Qiuyi Luo summarized the results of the study in a press release. “In a word, we found that binary / multiple stars tend to form in denser and more turbulent molecular nuclei in this study.”
Co-author Sheng-Yuan Liu added, “JCMT has proven to be an excellent tool for uncovering these amazing nurseries for ALMA follow-ups. a more thorough understanding of star formation. “
The researchers also found that the stars in each binary or multiple arrangement are usually in very different evolutionary stages. The more developed protostars are generally further from the center of the dense nuclei than their younger counterparts. This indicates that as the stars evolve, they migrate out of their birth cores.
This study shows some differences between nuclei that form single stars and nuclei that form binary and multiple stars. But that’s just the beginning: there is much more to learn and many more questions.
One of the questions is what role does magnetic field play in star formation? Star-forming clouds can be highly magnetized. Magnetic fields from the interstellar medium penetrate star-forming clouds, and astronomers know that magnetic fields can affect the rate of star formation. Do they play a role in determining whether a single star is formed versus several stars?
“We have not yet looked at the effect of magnetic fields in our analysis,” says corresponding author Tie Liu, who was also the leader of the ALMA observations. “Magnetic fields can suppress fragmentation in dense nuclei, so we are pleased to focus the next step of our research in this area with JCMT.”
The authors point out that the low sample size inhibits their results. Forty-three dense nuclei may not have enough data to draw conclusions from, especially since they are all from the same molecular cloud. The study was also limited by the resolution of the various observatories and telescopes used in the study.
“Our results could be further tested using future observations with higher spatial and spectral resolution against a more complete dense core sample in different molecular clouds found in widely differing environments,” they conclude.