When something burns up in atmosphere it’s not due to friction

When something burns up in atmosphere, it’s not due to friction. The heat is generated due to extreme compression caused by the Ram Pressure as the object forces its way through the atmosphere at high speed


In physics, ram pressure is a pressure exerted on a body which is moving through a fluid medium. It causes a strong drag force to be exerted on the body. It is given by:


where P is the pressure, is the density of the fluid and v the velocity of the body. Alternatively the body can be stationary and v describe the velocity of the fluid, e.g. the solar wind.

For example, a meteor traveling through the Earth’s atmosphere produces a shock wave generated by the extremely rapid compression of air in front of the meteoroid. It is primarily this ram pressure (rather than friction) which heats the air which in turn heats the meteoroid as it flows around it.

Galaxies in clusters experience ram pressure as they move through the intracluster medium; it is capable of stripping the galaxy of much of its interstellar gas

A galaxy passing through the ICM feels an external pressure. This pressure depends on the ICM density ICM and the relative velocity vrel of the galaxy and the ICM. Gunn & Gott (1972) suggested this process already many years ago. They also gave a frequently used prescription for the radius r beyond which the gas of a galaxy is stripped, depending on the ram pressure and the galactic gravitational restoring force. The implicit condition on r reads

with pram being the ram pressure, G the gravitational constant, star the stellar surface density, gas the surface mass density of the galactic gas.

An analytical model has been developed to describe ram-pressure stripping for galaxies of different morphologies in different environments (Hester 2006). It describes the stripping of a satellite galaxy’s outer H I disk and hot galactic halo.



As ram-pressure stripping is such a common process, there are many simulations in which the stripping process of galaxies was calculated for different types of galaxies: spirals, ellipticals and dwarfs (Abadi et al. 1999, Quilis et al. 2000, Mori & Burkert 2000, Toniazzo & Schindler 2001, Schulz & Struck 2001, Vollmer et al. 2001, Hidaka & Sofue 2002, Bekki & Couch 2003, Otmianowska-Mazur & Vollmer 2003, Acreman et al. 2003, Marcolini et al. 2003, Roediger & Hensler 2005, Roediger & Brüggen 2006, Roediger et al. 2006, Mayer et al. 2006, Vollmer et al. 2006, see Fig. 2). The simulations confirm that the process is acting in the expected way. Starting from the outer parts of the galaxy gas is stripped off. Part of this gas is not bound to the galaxies anymore and left in a wide (fragmenting) tail behind the galaxy. Recently even the increase of star formation in and behind the galaxy caused by ram-pressure stripping has been found in simulations (Kronberger et al. 2008a, Kapferer et al. 2008). Brüggen et al. (2008) found that more than half of the cluster galaxies have experienced ram-pressure stripping and hence a considerable fraction of galaxies in a cluster at the present epoch has suffered a substantial gas loss.

It was tested with simulations whether the simple, widely used criterion by Gunn & Gott (1972) is a good estimate for the mass loss. Generally it is found that the criterion is a good estimate for the mass loss (Roediger & Brüggen 2007b, Kronberger et al. 2008a) when simulations and analytic estimates are compared for the same conditions (see Jachym et al. 2007 for a comparison with different conditions) – a quite surprising result given the simple assumptions of the criterion, that do not even take into account dark matter.