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Reference.org
Protoplanetary disk
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<p>A protoplanetary disk is a rotating <a href="/facts/Circumstellar_disc/aEr3EdJF">circumstellar disc</a> of dense gas and dust surrounding a <a href="/facts/Stellar_evolution/Qa4vAGmn">young newly formed</a> star, a <a href="/facts/T_Tauri_star/vX5WL56u">T Tauri star</a>, or <a href="/facts/Herbig_Ae/Be_star/E5NPDj8K">Herbig Ae/Be star</a>. The protoplanetary disk may not be considered an <a href="/facts/Accretion_disk/8zJXshat">accretion disk</a>; while the two are similar, an accretion disk is hotter and spins much faster; it is also found on <a href="/facts/Black_hole/1r2lmkcF">black holes</a>, not stars. This process should not be confused with the accretion process thought to build up the planets themselves. Externally illuminated photo-evaporating protoplanetary disks are called <a href="/facts/Proplyds/nsgTPq43">proplyds</a>. </p>