請確認是不是galaxy那篇

garyku

google 找的
感覺很類似

Clusters of galaxies are the largest gravitationally bound virialized objects in the universe.

They are filled with hot X-ray gas with temperatures of » 2–10 keV. The gas is

thought to be heated by the energy released when clusters gravitationally collapsed. While

the gas cooling through the X-ray radiation is inefficient in most regions of a cluster, it is

very efficient in the central region because of the high gas density. From X-ray observations,

it can be estimated that the thermal energy of the gas within cluster cores is lost radiatively

within » 108¡9 yr. The gas cooling should decrease the temperature and pressure of the gas

at the cluster cores, and the weight of the overlying gas should produce gas flows toward the

cluster centers. The flows are called “cooling flows” and the idea has prevailed for about 30

years (Fabian 1994).

Recent X-ray observations showed that the gas in the central regions of clusters is not

cooling as much as previously believed. This is indicated by the lack of metal line emission

that is characteristic of cooling X-ray gas (e.g. Ikebe et al. 1997; Makishima et al. 2001;

Peterson et al. 2001; Tamura et al. 2001; Kaastra et al. 2001; Matsushita et al. 2002). This

means that the above simple cooling flow picture is not correct and that there must be some

heating sources balancing the energy loss through X-ray emission in the central regions of

clusters.

There are several heating models such as heat conduction (e.g. Takahara & Takahara

1981; Tucker & Rosner 1983; Friaca 1986; Gaetz 1989; B¨ohringer & Fabian 1989; Sparks 1992;

Saito & Shigeyama 1999; Narayan & Medvedev 2001), acoustic waves propagating from the

outside of a cluster core (Fujita, Suzuki, & Wada 2004), or magnetohydrodynamic (MHD)

effects (Makishima et al. 2001). At present, the most promising candidate for the heating

source is the supermassive black hole at the center of the giant elliptical cluster-center galaxy

(e.g. Tucker & Rosner 1983; Rephaeli 1987; B¨ohringer & Morfill 1988; Binney & Tabor 1995;

Soker et al. 2001; Ciotti & Ostriker 2001; B¨ohringer et al. 2002; Churazov et al. 2002; Soker,

Blanton, & Sarazin 2002; Reynolds, Heinz, & Begelman 2002; Kaiser & Binney 2003). In

fact, the Chandra X-ray observatory has shown that the strong activities of the supermassive

black holes disturb hot X-ray gas in the central regions of clusters (e.g. Fabian et al. 2000;

McNamara et al. 2000; Blanton et al. 2001; McNamara et al. 2001; Mazzotta et al. 2002;

Fujita et al. 2002; Johnstone et al. 2002; Kempner, Sarazin, & Ricker 2002; Takizawa et al.

2003). In many clusters, bubbles of high energy particles have been found; it is expected that

jets produced by the supermassive black holes inflate those bubbles. Moreover, numerical

simulations have suggested that the bubbles move outward in a cluster by buoyancy, thus

mixing the surrounding hot X-ray gas (e.g. Churazov et al. 2001; Quilis, Bower, & Balogh

2001; Saxton, Sutherland, & Bicknell 2001; Br¨uggen & Kaiser 2002; Basson & Alexander

2003). As a result of the mixing, hot X-ray gas in the outer region of the cluster is brought

into, and subsequently heats the cluster center. Moreover, Chandra found that acoustic

waves formed through jet activities are propagating in the hot X-ray gas of the Perseus

cluster (Fabian et al. 2003). Through the viscosity of the gas, the waves may heat the

surrounding gas.

» 2–10 keV. The gas is

thought to be heated by the energy released when clusters gravitationally collapsed. While

the gas cooling through the X-ray radiation is inefficient in most regions of a cluster, it is

very efficient in the central region because of the high gas density. From X-ray observations,

it can be estimated that the thermal energy of the gas within cluster cores is lost radiatively

within » 108¡9 yr. The gas cooling should decrease the temperature and pressure of the gas

at the cluster cores, and the weight of the overlying gas should produce gas flows toward the

cluster centers. The flows are called “cooling flows” and the idea has prevailed for about 30

years (Fabian 1994).

Recent X-ray observations showed that the gas in the central regions of clusters is not

cooling as much as previously believed. This is indicated by the lack of metal line emission

that is characteristic of cooling X-ray gas (e.g. Ikebe et al. 1997; Makishima et al. 2001;

Peterson et al. 2001; Tamura et al. 2001; Kaastra et al. 2001; Matsushita et al. 2002). This

means that the above simple cooling flow picture is not correct and that there must be some

heating sources balancing the energy loss through X-ray emission in the central regions of

clusters.

There are several heating models such as heat conduction (e.g. Takahara & Takahara

1981; Tucker & Rosner 1983; Friaca 1986; Gaetz 1989; B¨ohringer & Fabian 1989; Sparks 1992;

Saito & Shigeyama 1999; Narayan & Medvedev 2001), acoustic waves propagating from the

outside of a cluster core (Fujita, Suzuki, & Wada 2004), or magnetohydrodynamic (MHD)

effects (Makishima et al. 2001). At present, the most promising candidate for the heating

source is the supermassive black hole at the center of the giant elliptical cluster-center galaxy

(e.g. Tucker & Rosner 1983; Rephaeli 1987; B¨ohringer & Morfill 1988; Binney & Tabor 1995;

Soker et al. 2001; Ciotti & Ostriker 2001; B¨ohringer et al. 2002; Churazov et al. 2002; Soker,

Blanton, & Sarazin 2002; Reynolds, Heinz, & Begelman 2002; Kaiser & Binney 2003). In

fact, the Chandra X-ray observatory has shown that the strong activities of the supermassive

black holes disturb hot X-ray gas in the central regions of clusters (e.g. Fabian et al. 2000;

McNamara et al. 2000; Blanton et al. 2001; McNamara et al. 2001; Mazzotta et al. 2002;

Fujita et al. 2002; Johnstone et al. 2002; Kempner, Sarazin, & Ricker 2002; Takizawa et al.

2003). In many clusters, bubbles of high energy particles have been found; it is expected that

jets produced by the supermassive black holes inflate those bubbles. Moreover, numerical

simulations have suggested that the bubbles move outward in a cluster by buoyancy, thus

mixing the surrounding hot X-ray gas (e.g. Churazov et al. 2001; Quilis, Bower, & Balogh

2001; Saxton, Sutherland, & Bicknell 2001; Br¨uggen & Kaiser 2002; Basson & Alexander

2003). As a result of the mixing, hot X-ray gas in the outer region of the cluster is brought

into, and subsequently heats the cluster center. Moreover, Chandra found that acoustic

waves formed through jet activities are propagating in the hot X-ray gas of the Perseus

cluster (Fabian et al. 2003). Through the viscosity of the gas, the waves may heat the

surrounding gas.

» 108¡9 yr. The gas cooling should decrease the temperature and pressure of the gas

at the cluster cores, and the weight of the overlying gas should produce gas flows toward the

cluster centers. The flows are called “cooling flows” and the idea has prevailed for about 30

years (Fabian 1994).

Recent X-ray observations showed that the gas in the central regions of clusters is not

cooling as much as previously believed. This is indicated by the lack of metal line emission

that is characteristic of cooling X-ray gas (e.g. Ikebe et al. 1997; Makishima et al. 2001;

Peterson et al. 2001; Tamura et al. 2001; Kaastra et al. 2001; Matsushita et al. 2002). This

means that the above simple cooling flow picture is not correct and that there must be some

heating sources balancing the energy loss through X-ray emission in the central regions of

clusters.

There are several heating models such as heat conduction (e.g. Takahara & Takahara

1981; Tucker & Rosner 1983; Friaca 1986; Gaetz 1989; B¨ohringer & Fabian 1989; Sparks 1992;

Saito & Shigeyama 1999; Narayan & Medvedev 2001), acoustic waves propagating from the

outside of a cluster core (Fujita, Suzuki, & Wada 2004), or magnetohydrodynamic (MHD)

effects (Makishima et al. 2001). At present, the most promising candidate for the heating

source is the supermassive black hole at the center of the giant elliptical cluster-center galaxy

(e.g. Tucker & Rosner 1983; Rephaeli 1987; B¨ohringer & Morfill 1988; Binney & Tabor 1995;

Soker et al. 2001; Ciotti & Ostriker 2001; B¨ohringer et al. 2002; Churazov et al. 2002; Soker,

Blanton, & Sarazin 2002; Reynolds, Heinz, & Begelman 2002; Kaiser & Binney 2003). In

fact, the Chandra X-ray observatory has shown that the strong activities of the supermassive

black holes disturb hot X-ray gas in the central regions of clusters (e.g. Fabian et al. 2000;

McNamara et al. 2000; Blanton et al. 2001; McNamara et al. 2001; Mazzotta et al. 2002;

Fujita et al. 2002; Johnstone et al. 2002; Kempner, Sarazin, & Ricker 2002; Takizawa et al.

2003). In many clusters, bubbles of high energy particles have been found; it is expected that

jets produced by the supermassive black holes inflate those bubbles. Moreover, numerical

simulations have suggested that the bubbles move outward in a cluster by buoyancy, thus

mixing the surrounding hot X-ray gas (e.g. Churazov et al. 2001; Quilis, Bower, & Balogh

2001; Saxton, Sutherland, & Bicknell 2001; Br¨uggen & Kaiser 2002; Basson & Alexander

2003). As a result of the mixing, hot X-ray gas in the outer region of the cluster is brought

into, and subsequently heats the cluster center. Moreover, Chandra found that acoustic

waves formed through jet activities are propagating in the hot X-ray gas of the Perseus

cluster (Fabian et al. 2003). Through the viscosity of the gas, the waves may heat the

surrounding gas.

Chandra X-ray observatory has shown that the strong activities of the supermassive

black holes disturb hot X-ray gas in the central regions of clusters (e.g. Fabian et al. 2000;

McNamara et al. 2000; Blanton et al. 2001; McNamara et al. 2001; Mazzotta et al. 2002;

Fujita et al. 2002; Johnstone et al. 2002; Kempner, Sarazin, & Ricker 2002; Takizawa et al.

2003). In many clusters, bubbles of high energy particles have been found; it is expected that

jets produced by the supermassive black holes inflate those bubbles. Moreover, numerical

simulations have suggested that the bubbles move outward in a cluster by buoyancy, thus

mixing the surrounding hot X-ray gas (e.g. Churazov et al. 2001; Quilis, Bower, & Balogh

2001; Saxton, Sutherland, & Bicknell 2001; Br¨uggen & Kaiser 2002; Basson & Alexander

2003). As a result of the mixing, hot X-ray gas in the outer region of the cluster is brought

into, and subsequently heats the cluster center. Moreover, Chandra found that acoustic

waves formed through jet activities are propagating in the hot X-ray gas of the Perseus

cluster (Fabian et al. 2003). Through the viscosity of the gas, the waves may heat the

surrounding gas.

Chandra found that acoustic

waves formed through jet activities are propagating in the hot X-ray gas of the Perseus

cluster (Fabian et al. 2003). Through the viscosity of the gas, the waves may heat the

surrounding gas.

camelo777

这篇我也找过了，好像不是，不过还是请考到的同学确认下~

Bale

有点略长……