MPIA Picture of the month

Massive star formation

Fri, 26 Feb 2010 10:30:00 +0100

Legend:

Contour lines	=	Gas-density
Colors	=	Temperature

Description:
In the related research project (MSF), we investigate the role of the radiation pressure onto the formation of massive stars. Potentially, the strong radiation pressure of a massive star inhibits further accretion onto its surface; such an intrinsic process would e.g. give an upper mass limit for stars in general.
The image illustrates a snapshot of a high-resolution radiation hydrodynamics simulation of the collapse of a pre-stellar core of cold gas and dust of 120 solar masses. In the center of the core, a new star is born during the free-fall epoch of the collapsing core. Afterwards the newborn star gains further mass from an accretion disk, which formed due to angular momentum conservation from the initially slowly rotating core.
After some while, the luminosity of the massive star has increased so much, that the resulting radiation pressure drags the in-falling mass from the bipolar direction into outer space. The concentrated opaque density of the accretion disk (the blue region) hampers the radiation pressure in this midplane layer at this point in time.
At the point when the accretion from the envelope region onto the disk has sufficiently decreased, the accretion disk looses its opaqueness and without this shielding effect the radiation pressure of the star starts to clear also the midplane layer.
In the end, the final star has accreted approximately 56.5 solar masses.

Authors:
Rolf Kuiper

More information:
Homepage of the author
Scientific background
YouTube channel

Anchoring Magnetic Field in Turbulent Molecular Clouds

Wed, 03 Dec 2009 13:12:00 +0100

The background image shows the far-infrared map in representative color and logarithmic scale. Superposed on it are the magnetic field directions inferred from optical polarimetry data (blue lines) tracing the diffused regions. The average of all the optical data is shown as the thick gray line. Magnetic fields within eight high-density cloud cores (labels A through H on the background map) are mapped using submillimeter polarimetry and the results are shown as insets, using red lines on individual representative-color intensity maps. The average direction of each core is shown as a white line superposed on the core map; these white lines also are plotted on the background map. Even though the core separations exceed the core sizes by as much as a factor of 100, they are for the most part "magnetically connected", i.e. the cores' average field directions are similar. Moreover, these directions are close to the average field direction seen in the diffused regions, as seen in a cloud simulation with sub-Alfvenic turbulence.

Authors:
Hua-bai Li (MPIA); Darren Dowell (JPL/Caltech); Alyssa Goodman (CfA); Roger Hildebrand (U. Chicago); and Giles Novak (Northwestern U.)

Reference:
Link to the article

Clustering in massive star forming regions

Mon, 05 Oct 2009 11:05:00 +0100

Despite their importance, the formation and early evolution of massive mass stars (more massive than 8 times the mass of the Sun) is not well understood. The formation and early evolution of high-mass stars happens in clustered and highly complex environments, where the forming stars and the molecular cloud are mutually interacting. To properly understand the role of the cluster in the formation of massive stars we need to investigate the complete stellar content of these regions. This figure shows a Spitzer/IRAC image of RCW 34, a massive star-forming region (blue: 3.6 micron, green: 4.5 micron, red: 8 micron) located in the Vela Molecular Cloud. A large bubble has been detected on the IRAC images in which a cluster of intermediate- and low-mass class II objects is found. Surprisingly, the massive stars are not present in the center of the bubble, but at the northern edge only, where an HII region is located, ionized by 3 massive stars. North of the HII region, a dense molecular cloud is detected where current star formation is still taking place. To explain this unusual location of the massive stars we have to conclude that this complex region is not formed in one star formation event, but the large bubble is formed first, and only after that the massive stars are formed. Currently, the stars inside the molecular cloud north of the bubble are still forming.

Authors:
Arjan Bik, Thomas Henning, Tatiana Vasyunina, Henrik Beuther, Hendrik Linz, paper submitted

Large Rotational Structure in a Massive Star Formation Region

Fri, 31 Aug 2009 15:52:00 +0100

These are velocity moment maps of three different higher density molecular tracers. At each spatial position, a velocity moment map plots the intensity weighted velocity of the respective line from that location. The source, IRDC 18223-3 is at the beginning of the massive star formation process. We first identified the outflow orientation using 12CO to be in the northwest-southeast direction (indicated on the plots with arrows). All of these molecules exhibit a velocity gradient that is not aligned with that outflow orientation. We suspect that C18O may be influenced by the outflow, but the other lines show a velocity gradient perpendicular to the outflow orientation. This is indicative of rotation perpendicular to the outflow likely resulting from a large rotating and infalling envelope (diameter ~28,000 AU) that may harbor a smaller Keplerian disk within.

Open House at MPIA

Wed, 28 May 2009 16:13:00 +0100

Sunday, March 17 was Open House Day at the Max-Planck-Institute for Astronomy. Around 5000 visitors took the effort of getting up on the hill to look at exhibitions, try out experiments, listen to talks or to talk to the astronomers.

The PSF department has contributed many public talks, a corner with experiments, video presentations and posters and a ''timeline'' of 9 posters describing the various aspects of planet and star formation.

Due to the enormous interest in these posters, we have decided to make them available on this page (click on the images below for hi-res pdf files). You can find also a link to a video showing some impressions of the Open House Day 2009.

Vortices as efficient particle traps

Wed, 1 Apr 2009 14:25:00 +0100

To date, 344 exoplanets have been found from which 89 are in multiple-planet systems. There are altogether 37 systems with more than 1 detected planet (www.exoplanet.eu). The question naturally arises whether the formation of a first planet helps to form other planets in the system?
Would these multiple systems be frequent or rare?
A giant planet opens up a gap in the disk. Also vortices can form at the outer edges of the gap, if the disk is not too turbulent. These vortices then merge and soon there will be one big vortex at the outer edge of the gap, and a smaller one at the inner edge of the gap. These vortices can trap the dust particles and if the relative velocity between these particles are low enough, they will collide and grow producing planet cores.

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A possible environment for planet formation

Wed, 4 Mar 2009 13:01:00 +0100

Protoplanetary disks are often tought to be turbulent and having a pressure that decreases with radius. This scenario leads to inward drift of the particles (due to the pressure gradient) and to fragmentation of the particles (due to the turbulence).

One possible way to keep particles growing in the disk are so called dead zones. The turbulence is driven by magnetic fields which couple to the ionized gas. Reducing the ionization fraction can cause the turbulence to stop working. Gas therefore accumulates in dead zones. If this causes a pressure bump, particles will stop drifting, once they reach the dead zone.
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[Ne II] emission in T Tau

Tue, 10 Feb 2009 12:18:00 +0100

Emission from ionized neon in the 12.81 micrometer [Ne II] line is observed towards many young stars. It has been thought to originate in the surface of their circumstellar disks, which are irradiated by X-rays from the central star. However, an alternative emission mechanism has been proposed: [Ne II] production in shocks occuring e.g. in jets.
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Brown Dwarfs Don't Hang Out With Stars

Fri, 09 Jan 2009 16:22:00 +0100

This pair of NASA Hubble Space Telescope images of the binary brown dwarf Kelu-1 trace the orbital motion of the two stars over a seven-year span as photographed by the Near Infrared Camera and Multi-Object Spectrometer (NICMOS) on Hubble.

In 1998, the "stars" were too close together to be resolved by Hubble. By 2005, they had moved apart to a separation of 520 million miles. The projected maximum separation is 550 million miles.

Binary systems allow astronomers to estimate the mass of companion objects. The brown dwarfs are 61 and 50 times the mass of Jupiter. They are therefore too small to burn as stars, but too large to have formed as planets. Based on the total estimated mass of the system, astronomers suspect there is a third brown dwarf member that has not yet been resolved.
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Simulation of the diversity of extrasolar planets

Mon, 01 Dec 2008 08:55:00 +0100

According to our current understanding form planets in circumstellar disks of dust and gas, where dust particles first accumulate to form kilometer sized planetesimals, and then continue to grow first to protoplanets and finally to planets with some mass and distance from the parent star.
These model calculations show which planetary masses are expected at which distances from a solar like star. The numerical formation model contains our current knowledge about dust and gas disks around young stars as well as present-day theories about various planet formation processes.
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Plasma beta in saturated MRI turbulence

Tue, 04 Nov 2008 20:55:00 -0800

This contour plot presents the logarithmic plasma beta distribution in the saturated MRI turbulence regime. The plasma beta describes the ratio between the gas pressure over the magnetic pressure.
There are low plasma beta regions (dark) with strong magnetic fields in the outer part of the disk and a dominating MRI turbulent core with weak magnetic fields (bigger plasma beta).

PSF Group Picture

Tue, 04 Nov 2008 17:20:07 -0800

Group picture from PSF Workshop 2008 at the monastery of Maulbronn