Star collision movies

James Lombardi
Allegheny College

Below is a sampling of visualizations of various stellar collisions and mergers. To save any to your computer, right click on the link and choose "Save link as...." Use freely, but please give appropriate credit.

Formation of Stripped Stars From Stellar Collisions in Galactic Nuclei

Galactic nuclei provide an environment for high-velocity stellar collisions that strip the carbon- and hydrogen-rich envelopes of the stars involved and leave behind enhanced nitrogen cores. The following column-density visualizations are from simulations of 3 solar mass terminal age main-sequence star colliding with a 2 solar mass main-sequence star of comparable age (Gibson et al. 2024, submitted).

Case 6 (mp4 file): Head-on collision with a velocity at infinity of 3500 km/s. The stars merge to form a 0.48 solar mass product.
Case 32 (mp4 file): An off-axis (specifically, 0.7 solar radius periastron separation) collision with a 5000 km/s velocity at infinity, resulting in two collisionally stripped stars. The panel on the left focuses on material from the 3 solar mass parent star, while the panel on the right focuses on that of the 2 solar mass parent.
Case 33 (mp4 file): This is like the previous off-axis collision (still a 0.7 solar radius periastron separation) but now at 6000 km/s. Only a single stripped star results, as the lower mass star is destroyed by the encounter.

Twin Binaries: Studies of Stability, Mass Transfer, and Coalescence

Mergers of binaries can ultimately lead to the formation of exotic systems such as binary neutron stars or planetary nebulae with double degenerate cores. These visualizations are from simulations published in Lombardi, Holtzman, Dooley, Gearity, Kalogera, & Rasio (2011) and are shown in a frame rotating with a period nearly matching the initial orbital period.

mpeg file (76 MB): The merger of two identical red giant stars, each with a core mass equal to 20% of its total mass, from initial conditions just inside the Roche limit (that is, the innermost equilibrium configuration). The centers of the stars are initially separated by 2.20 times the radius each would have in isolation. Mass shedding through the outer Lagrangian points drives a rapid merger. The frame rotates with a period of ~14 in our units. See Figure 12 and the associated text of Lombardi et. al (2011) for more details.
mpeg file (7.2 MB): In contrast to the preceeding visualization, which is at a slightly smaller initial separation, this red giant contact binary at a separation of 2.22 is in a stable equilibrium state. The frame rotates with a period of ~15, which nearly matches the orbital period of the binary. During the ~30 orbits covered by the visualization, there are no significant changes to the stucture of the binary.
mpeg file (83 MB): The merger of two identical stars, each with a core mass equal to 5% of its total mass, in an unstable contact binary. The centers of the stars are initially separated by 2.54 times the radius each would have in isolation. The mass transfer develops slowly at first, but the merger itself is rapid. The time in the visualization (see the upper left corner) advances less quickly during the merger simply to make the fluid motion during that interval easier to observe. The frame rotates with a period of ~18 in our units. See Figure 10 and the associated text of Lombardi et. al (2011) for more details.
mpeg file (26 MB): In contrast to the preceeding visualization, which is at a slightly smaller separation, this contact binary with initial separation 2.56 is stable. The frame rotates with a period of ~18. During the nearly 100 orbits covered by the visualization, there are no significant changes to the stucture of the binary.

Blue straggler formation

Given the the great age of clusters, it was predicted that stars more massive than about 80% the mass of the Sun, the so-called turnoff mass, should have evolved to later stages of stellar life, ultimately "dying" off as a dim stellar remnant such as a white dwarf, neutron star, or black hole. Nevertheless, when one observes a globular cluster, a number of bluish main-sequence stars, more massive than the turnoff mass, are seen scattered throughout. These "blue stragglers" appear to 'straggle' behind in their evolution, since, despite being more massive than the turnoff mass, they have not yet left the main-sequence.

The calculations performed by Alexander Brown '09 and Lombardi help establish that these exotic blue stragglers can indeed be formed through the collision of garden-variety main-sequence stars in a cluster. Visualizations of one of their simulations were featured in two recent episodes of a History Channel series entitled "The Universe."

Here we provide visualizations and individual frames of a collision between a 0.8 and a 0.7 solar mass star at a periastron separation of 0.89 solar radii. The file size of these particular movies and frames exceed 100 MB, so be patient!
Quicktime movie, jpeg's of frames (zipped): 2D cross section in orbital plane with colors representing density. (Very large files!)
Quicktime movie, jpeg's of frames (zipped): Line of sight view with colors representing column density. (Very large files!)

mov file: collision between a 0.8 solar mass and 0.6 solar mass star. Clip is from the "Cosmic Collision" skyshow shown at the Hayden planetarium, the National Air and Space Museum, the Museum of Nature and Science, and the Shanghai Science and Technology Museum.
avi file: the different colors represent different constant density surfaces. The top halves of the outer two isodensity surfaces have been removed so that we can see deep into the stars.
mpeg file: collision between a 0.8 and a 0.6 solar mass star at a periastron separation of 0.37 solar radii. 2D cross section in orbital plane with colors representing density.

avi file: 3D particle plot showing the first collision in a triple star merger.
mov file: 3D particle plot showing the second collision in a triple star merger.

Ultracompact X-ray binary formation

Collisions between neutron stars and subgiants can lead to the formation of ultracompact x-ray binaries. These visualizations present hydrodynamics calculations of a collision between a 1.4 solar mass neutron star and an 0.9 solar mass subgiant star, on initially parabolic trajectories with a periastron separation of 3.8 solar radii. Colors correspond to the column density of the fluid along the line of sight.
mov file: Periastron separation of 1.9 solar radii.
mov file: Periastron separation of 3.8 solar radii.

Intermediate mass black hole formation

Runaway collisions involving high mass main-sequence stars in young star clusters may ultimately lead to the formation of intermediate mass black holes.
mov file: 106 and 77 solar mass stars colliding with a periastron separation of 24 solar radii and an orbital eccentricity of 1.02 (from Valerie McVay's comp).

This next visualizations, made in collaboration with Scott Fleming and Katherine Dooley, present hydrodynamics calculations of a collision between a 53 solar mass and an 18 solar mass star, with an orbital eccentricity of 0.68 and periastron separation of 23 solar radii (see the March 2004 Astronomy Magazine). Initial conditions were taken from the first stellar collision in a runaway sequence in a cluster dynamics simulation by Portegies Zwart et al., at a time of 3.0 Myr. The stellar models were taken from stellar evolution calculations by D. Arnett's Tycho code. The visualization is given a three-dimensional feel by assigning colors according to the column density of the fluid along the line of sight:
512x384 mov file: radiation and ideal gas pressure included.
1000x750 mov file: ideal gas only.

Learn More

Outreach links: Popular short summaries, informative pictures and animations, and press release type statements relevant to MODEST (Modeling Dense Stellar Systems).
Stellar collision research at Allegheny: Links regarding our group's research.

Last updated: May 2024

James Lombardi Allegheny College