I’ve always had a passion for origins, which is why I once pondered a career in paleontology. The idea of working at an excavation where I could examine the remains of things that had lived hundreds of millions of years ago was galvanizing, and I read deeply into what we knew about the planet’s earliest creatures. Later, understanding that the most distant objects we see are also the oldest, I transferred that passion for origins into an interest in cosmology.
So a recent finding out of the University of Illinois at Urbana-Champaign is heady stuff indeed. There, astonomers Leslie Looney, Brian Fields and a sharp undergraduate named John Tobin have been studying the birth of our Sun by looking at the descendants — ‘daughter species’ — of the short-lived radioactive isotopes found in early meteorites. The isotopes themselves are created in supernova explosions; they become mixed with the nebular gas and dust that will eventually condense into stars, planets and debris like meteorites.
The picture that emerges is striking. A massive star whose distance can be roughly calculated from the abundances of these daughter species blew up from within a cluster of hundreds or perhaps thousands of low-mass stars like the Sun. “The supernova was stunningly close; much closer to the sun than any star is today,” said Fields. “Our solar system was still in the process of forming when the supernova occurred.”
The study looks at probable distances in two scenarios. If the supernova and our Sun formed at around the same time, then the astronomers calculate the distance between the Solar nebula and the supernova ranged from 0.1 to 1.6 parsecs. If the supernova actually triggered the Sun’s later formation, the distances can go as high as 4 parsecs. “This sounds surprisingly close,” write Looney and Fields, “but it is consistent with typical distances found for low-mass stars clustering around one or more massive stars. We posit that our Sun was a member of such a cluster that has since dispersed.”
What this work implies is that planetary systems are resilient enough to weather such catastrophes, an indication that even in roiling stellar nurseries, the early rounds of planet formation should not be ruled out. The stars which formed near the Sun have moved away over the eons, but it’s a working assumption that the majority of stars in the galaxy came out of star clusters like these. And that would make our Solar System a relatively common example of planetary formation, still more evidence that the galaxy at large must be teeming with systems that can weather and build upon nearby cosmic cataclysms.
The preprint of Looney, et al., “Radioactive Probes of the Supernova-Contaminated Solar Nebula: Evidence that the Sun was Born in a Cluster” can be found here. The paper has been accepted for publication in the Astrophysical Journal.
On the likelihood of supernova enrichment of protoplanetary disks
Authors: Jonathan P. Williams, Eric Gaidos (Univ. of Hawaii Manoa)
(Submitted on 24 May 2007)
Abstract: We estimate the likelihood of direct injection of supernova ejecta into protoplanetary disks using a model in which the number of stars with disks decreases linearly with time, and clusters expand linearly with time such that their surface density is independent of stellar number. The similarity of disk dissipation and main sequence lifetimes implies that the typical supernova progenitor is very massive, ~ 75-100 Msun. Such massive stars are found only in clusters with > 10^4 members. Moreover, there is only a small region around a supernova within which disks can survive the blast yet be enriched to the level observed in the Solar System. These two factors limit the overall likelihood of supernova enrichment of a protoplanetary disk to
Injection of Short-Lived Radionuclides into the Early Solar System from a Faint Supernova with Mixing-Fallback
Authors: A. Takigawa, J. Miki, S. Tachibana, G. R. Huss, N. Tominaga, H. Umeda, K. Nomoto
(Submitted on 11 Aug 2008)
Abstract: Several short-lived radionuclides (SLRs) were present in the early solar system, some of which should have formed just prior to or soon after the solar system formation. Stellar nucleosynthesis has been proposed as the mechanism for production of SLRs in the solar system, but no appropriate stellar source has been found to explain the abundances of all solar system SLRs.
In this study, we propose a faint supernova with mixing and fallback as a stellar source of SLRs with mean lives of <5 Myr (26Al, 41Ca, 53Mn, and 60Fe) in the solar system. In such a supernova, the inner region of the exploding star experiences mixing, a small fraction of mixed materials is ejected, and the rest undergoes fallback onto the core. The modeled SLR abundances agree well with their solar system abundances if mixing-fallback occurs within the C/O-burning layer. In some cases, the initial solar system abundances of the SLRs can be reproduced within a factor of 2.
The dilution factor of supernova ejecta to the solar system materials is ~10E-4 and the time interval between the supernova explosion and the formation of oldest solid materials in the solar system is ~1 Myr. If the dilution occurred due to spherically symmetric expansion, a faint supernova should have occurred nearby the solar system forming region in a star cluster.
Comments: 14 pages, 4 figures
Subjects: Astrophysics (astro-ph)
Cite as: arXiv:0808.1441v1 [astro-ph]
Submission history
From: Aki Takigawa [view email]
[v1] Mon, 11 Aug 2008 03:40:30 GMT (1308kb)
http://arxiv.org/abs/0808.1441