Tonight's Sky
Sun
Sun
Moon
Moon
Mercury
Mercury
Venus
Venus
Mars
Mars
Jupiter
Jupiter
Saturn
Saturn

Tonight's Sky — Change location

OR

Searching...

Tonight's Sky — Select location

Tonight's Sky — Enter coordinates

° '
° '

I understand that new stars form out of mostly hydrogen with smaller amounts of heavier elements. If helium, carbon, oxygen, and other heavier elements were abundant enough to form stars, could they?

Steve McCullum, Hopkins, Minnesota
L1157_spitzer
Most young stars, like L1157, form out of primarily hydrogen. NASA/JPL-Caltech/UIUC
Hydrogen is by far the most abundant element in the universe. It constitutes roughly 90 percent of atoms in the Sun and in most stars. Helium ranks second, with nearly 9 percent. This leaves only 1 percent of the atoms remaining for the rest of the periodic table of elements. Not surprisingly then, the giant gas clouds that condense into stars are hydrogen-rich. Therefore, calculations about stellar formation usually consider only the physical conditions that will make hydrogen-rich nebulae start to collapse.

Gas clouds of nearly any composition could theoretically become susceptible to condensation, given the right combination of physical parameters (mostly temperature, density, and turbulent motions) of the clouds. Stars formed of elements other than hydrogen would have different masses and evolutionary histories than normal hydrogen-rich stars. For example, a helium-rich star would need to shrink to a size much smaller than a hydrogen one to achieve the extremely high densities and temperatures to begin fusion, and such stars would not live long compared to hydrogen-rich ones. Life as we understand it would not exist on a planet around a helium-rich star. And elements heavier than carbon would create stars even denser, hotter, and shorter-lived than helium ones.

Nearly pure helium and carbon stars do exist. But these are the ultra-compact remnant cores of former suns that started their lives mostly with hydrogen and gradually created the heavier elements. — Christopher Sneden, University of Texas at Austin
0

JOIN THE DISCUSSION

Read and share your comments on this article
Comment on this article
Want to leave a comment?
Only registered members of Astronomy.com are allowed to comment on this article. Registration is FREE and only takes a couple minutes.

Login or Register now.
0 comments
ADVERTISEMENT

FREE EMAIL NEWSLETTER

Receive news, sky-event information, observing tips, and more from Astronomy's weekly email newsletter. View our Privacy Policy.

ADVERTISEMENT
ADVERTISEMENT
RCLP_ASY_0919_mediumrectangle
NASA's greatest space probes. What Cassini, Juno, and New Horizons discovered on their missions.
Find us on Facebook