Hagai B. Perets

Assistant prof., Technion, Israel.


Research fields

Currently I'm working on the following fields in astrophsyics:

1. Stellar dynamics in galactic nuclei (near massive black holes)

I'm working on a variety of issues concerning the dynamics of stars and massive black holes in galactic nuclei. These include the effects of massive perturbres such as giant molecular clouds in galactic nuclei on the dynamics of stars near massive black holes. I have shown that such perturbers can shorten the relaxation time in galactic nuclei by orders of magnitudes. Such effect can induce an enhanced rate scattered stars and binary stars onto the massive black hole(s). This mechanism can explain the large number of young stars observed close to the massive black hole in our Galactic center as captured stars following binary disruption )see movie below). It could also solve the so called "last parsec problem" of binary massive blak hole mergers; stars scattered by massive perturbers can extract orbital energy from a binary massive blak hole and induce its coalescence in short times (much shorter than a Hubble time).

Below is a short movie I made to ilustrate a possible mechanism for the origin of the young S-stars close to the massive black hole in the Galactic center, and the ejection of hypervelocity stars. A stellar binary is disrupted by the tidal forces from the massive black hole (the varying point in the center). One star is capture in a close eccentric orbit around the massive black hole, while its companion is ejected at a high velocity to become a hypervelocity star. I'm currently working on understanding the evolution of stellar disks in galactic nuclei, and the role of star-formation on the distribution of stars around massive black holes.

2. Stellar dynamics in dense stellar systems

I'm exploring the dynamics of dense stellar systems where close encounters between stars and binaries play an importnat role. I'm studying the dependence of angular momentum change of stars to their stellar mass (some related to mass segregation effects but in respct to angular momentum rather than energy).

3. Triple stellar evolution

About 10-15 % of all stars reside in triple systems. Howver, basicaly almost no study have been done on the stellar evolution of such syatems. In such systems both dynamics and stellar evolution can interact to form unique type of systsems. I am exploring these issues with the aim of providing an understaning of triple systems. A first study on this issue has given rise to a novel route for the formation of blue stragglers, not studied before, which could explain their uniqe properties in open clusters (e.g. high binary fraction, period ecccentricity distribution of binary blue stragglers). In Perets & Fabrycky (2009) we suggested that blue stargglers are formed in triple systems in which the inner binary is driven to coalescence through Kozai cicles and tidal friction effects. A simple expectation from this scenario is a high binary fraction for blue stragglers (the merged inner binary has an outer companion), and their period-eccentricity distibution to be similar to that of the outer binary of triples. Below is a figure showing that most blue stargglers indeed follow such a strange distribution (strange in the sense of e.g. absence of binaries with periods below ~700 days, where as other binaries in the same clsusters do not show such a gap). The blue and green signs are binary blue stragglers, the red signs are the outer binaries of triples. Article

4. Solar-System dynamics, currently focused on asteroids and Kuiper Belt binaries

I'm exploring the long term evolution of binary minor planets both due to encounters with planets and other planetesimals in the early Solar system, and due to secular long term evolution, e.g. Kozai oscillations, which could change the eccentricity and inclination of currently observed binaries.

5. Planet formation

I'm working on several aspects of planet formation, including planetesimals encounters in a gaseous environment and the role of binary planetesimals in planet formation. The latter is somewhat similar to the role of binaries in dense stellar systems where binary encounters are the most important catalysys for physical collisions. In planetesimals disks these could correpond to enhanced collison and therefore enhance growth rate of plantesimals.

6. Planets in evolved binary systems

I study planetary systems in evolved binary star systems. In such systems an evolved star shed material onto its companion forming an accretion disk. Planets can interact with this new material an migrate or grow. It's possible that new planets can form in these accretion disks ahich have many similarities with protoplanetary disks. Such systems might therefore form "second generation" planets long after the stellar system was born. planets around the evolving star can migrate dure to the mass loss, but since both the companion star and the planet migrate at different rates, the planets might be caught into resonances. The figure below ilustarte some of these possibilities.

7. Runaway and hypervelocity stars

I'm exloring the mechanisms in which stars are ejected to high velocities and the observational constrants we can use to study them.

8. Supernovae

With my collaborators I've discovered a new type of supernovae, likely resulting from detonataion of a helium shell on a white dwarf. These supernovae are type Ib supernovae (showing helium), very faint, calium rich and are realted to old stellar populations (early type host galaxies).

Below are a few figures showing SN 2005E.
The first shows the location of SN 2005E, a type Ib supenova, far from any star-forming region, contrary to what we would expect from a core-collapse supernova (type Ib supernovae were thought to be only realted to core collapse of massive stars).

The unique position of SN 2005E in mass luminousity diagram is shown below. Article

Finally, the distribution of host galaxies for the group of supernovae resembling SN 2005E, inconsistent with core-collapse supernovae.Article

9. Astrochemistry and interstellar dust

I'm interested in astrochemistry on interstellar and planetary dust, and they way in which moleculs form on dust particles. I've analyzed laboratory data and used it to learn about such mechanisms in the interstellar medium and in Titan atmosphere.

I'm also interested in non-astrophysics related fields, including quantum optics and quantum random walks.

I've also worked a bit on genetic networks, but not very recently.

The cobble stones of black and white,
the flowers of amazing red,
the smell of every springing hour
and shining memories of May -

all for you,
to keep to take,
to think about your way.
To feel, to taste,
to see the light

of everlasting life and might.