X-ray insights into star and planet formation

Abstract

Although stars and planets form in cold environments, X-rays are produced in abundance by young stars. This review examines the implications of stellar X-rays for star and planet formation studies, highlighting the contributions of NASA's (National Aeronautics and Space Administration) Chandra X-ray Observatory. Seven topics are covered: X-rays from protostellar outflow shocks, X-rays from the youngest protostars, the stellar initial mass function, the structure of young stellar clusters, the fate of massive stellar winds, X-ray irradiation of protoplanetary disks, and X-ray flare effects on ancient meteorites. Chandra observations of star-forming regions often show dramatic star clusters, powerful magnetic reconnection flares, and parsec-scale diffuse plasma. X-ray selected samples of premain sequence stars significantly advance studies of star cluster formation, the stellar initial mass function, triggered starformation processes, and protoplanetary disk evolution. Although X-rays themselves may not play a critical role in the physics of star formation, they likely have important effects on protoplanetary disks by heating and ionizing disk gases.massive stars | planet formation | premain sequence stars | star formation | x-ray astronomy T hermodynamically, X-ray astronomy should have little to say concerning the origin of stars and planets which form in molecular clouds around T ∼ 10 K and protoplanetary disks around T ∼ 100-1; 000 K, respectively. It was thus unclear why the Orion nebula was found to be a spatially resolved source by early X-ray observatories (1). The answers began emerging with the focusing optics of the Einstein Observatory: Massive stars produce X-rays in their radiatively accelerated winds, and low-mass premain sequence (PMS) stars produce powerful magnetic reconnection flares (2, 3). Diffuse X-ray emission attributed to past supernova explosions was also seen in the most violent starburst regions (4).While progress was made in understanding these processes with the ROSAT and ASCA (Advanced Satellite for Cosmology and Astrophysics) observatories during the 1990s (5), the Chandra X-ray Observatory provided uniquely spectacular views of star-forming regions in X-rays. The subarcsecond imaging of the Chandra mirrors is needed to resolve crowded young stellar clusters (YSCs), and the four dimensions of data (right ascension, declination, energy, and arrival time for each photon) from the Advanced CCD Imaging Spectrometer (ACIS) characterize the emission processes (6, 7). Fig. 1 shows two ACIS images of nearby star-forming regions, one a typical YSC with hundreds of X-ray sources associated with PMS stars, and the other a richer YSC with thousands of X-ray stars and diffuse emission from shocked massive winds outflowing into the galactic interstellar medium.The decades witnessing these X-ray findings were also critical in advancing our understanding of star-formation processes. It became evident that star formation is far more complex than gravitational collapse of a spherical, quiescent cloud...

Detection of a giant flare displaying quasi-periodic pulsations from a pre-main-sequence M star by the Next Generation Transit Survey

“…Flares and associated Coronal Mass Ejections (CMEs) from pre-main sequence stars could have an important role in planetary formation and habitability. For example, these transient events have been proposed as a possible mechanism for the formation of chondrules found in meteorites (Feigelson 2010). The flash-melting of these rocks requires a transient heat source, which could be provided either by direct absorption of flare XUV irradiation (Shu et al 2001), or through a flare associated shock wave (Nakamoto et al 2005).…”

The complete far-infrared and submillimeter spectrum of the Class 0 protostar Serpens SMM1 obtained withHerschel

“…X-ray emission is also expected in low-mass YSOs (Stäuber et al 2006(Stäuber et al , 2007Feigelson 2010) and they produce internally generated UV radiation fields after collisions of energetic photoelectrons with H and H 2 (Maloney et al 1996;Hollenbach & Gorti 2009). Although X-ray detections with Chandra have been reported towards the nearby Serpens SMM5, SMM6 and S68Nb protostars (Winston et al 2007), the strength of any X-ray emission from Serpens SMM1 is unknown, possibly because of the high column density to the embedded source.…”

The Elephant Trunk Nebula and the Trumpler 37 cluster: contribution of triggered star formation to the total population of an H iiregion

“…Sugitani, Tamura & Ogura ; Ogura, Sugitani & Pickles ; Urquhart, Morgan & Thompson ). While longer wavelength surveys select principally the youngest stars undergoing accretion from dusty discs, X‐ray surveys efficiently select young stars due to enhanced magnetic reconnection flaring that extends to the main sequence (Feigelson ). In a few cases, Chandra observations have added the disc‐free pre‐main‐sequence (PMS) populations to TSF clouds (e.g.…”