Machos encyclopedia topics

Machos or Mahos Μάχος
Statistics
Prefecture:	Ilia
Province:	Ilia
Municipality:	Vartholomio
Municipal district:	Machos (seat)
Location: Latitude: Longitude:	37.883 (37° 52' 53") N 21.193 (21° 11' 33") E
Population: (2001) -Village: (Change from 1991) -percent of the municipal district: Percent of the municipal district:-Percent of the municipality: - Rank (Village):	470 (-214 or -31.3%) 8.78%
Altitude: -lowest: -centre:	10 m (northeast) 20 m about 50 m (west)
Postal code:	GR-270 50
Car designation (as of 2006):	`HA`

Geography

Location:

Latitude: 37.883 (37°52'53') N
Longitude: 21.193 (21°11'33') N

Postal code: 270 50
Elevation: about 20 m
Dialing code: +11+30-26230-2 (030-26230-2)

Population

Between 1981 and 1991, Machos experienced a gigantic growth and was the fastest growing villages in percentage, but declined nearly one-third in the 2001 census.

Year	Communal population	Change	Percent of the municipality	Village Ranking
1981	359	-	-	-
1991	684	+325 or +90.6%	-	-
2001	470	-214 or -31.3%	8.78%	3rd (municipality)

About Machos

The village has a school, a church, a plateia (square) and some restaurants. The village was partially linked in the 1970s and after the early-1990s is almost fully accessed by paved roads. The village never has a railway station because the train tracks used to run 1 km east. Much of the small community is covered with olive groves and some trees while the east has some mixed farming.

After World War II and the Greek Civil War, most of the population left for larger towns and cities especially Patras. Most of the buildings were not damaged. The population remained steady since the mid to late 20th century. Houses were stone-built until the 1950s and did not surpass modern-style homes until the 1980s.

External links

GTP - Machos
traveljournals.net - Machos
Map and aerial photos:

Street map information from: Mapquest, LiveLocal or Google or Yahoo! Maps
Satellite images: Google or Microsoft Virtual Earth - image now available

Coordinates:

Detection

A MACHO may be detected when it passes in front of or nearly in front of a star and the MACHO's gravity bends the light, causing the star to appear brighter in an example of gravitational lensing known as gravitational microlensing. Several groups have searched for MACHOs by searching for the microlensing amplification of light. These groups have ruled out dark matter being explained by MACHOs with mass in the range 0.00000001 solar masses to 100 solar masses. One group, the MACHO collaboration, claims to have found enough microlensing to predict the existence of many MACHOs with mass of about 0.5 solar masses, enough to make up perhaps 20% of the dark matter in the galaxy. This suggests that MACHOs could be white dwarfs or red dwarfs which have similar masses. However, red and white dwarfs are not completely dark; they do emit some light, and so can be searched for with the Hubble Telescope and with proper motion surveys. These searches have ruled out the possibility that these objects make up a significant fraction of dark matter in our galaxy. Another group, the EROS2 collaboration does not confirm the signal claims by the MACHO group. They did not find enough microlensing effect with a sensitivity higher by a factor 2.

Observations using the Hubble Space Telescope's NICMOS instrument showed that less than one percent of the halo mass is composed of red dwarfs. This corresponds to a negligible fraction of the dark matter halo mass. Therefore, the missing mass problem is not solved by MACHOs.

Types of MACHOs

MACHOs may sometimes be considered to include black holes. Black holes are truly black in that they emit no light and any light shined upon them is sucked in before any illumination could occur. It is thought possible that there is a halo of black holes surrounding the galaxy. A black hole can sometimes be detected by the halo of bright gas and dust that forms around it as an accretion disc being pulled in by the black hole's gravity. Such a disk can generate jets of gas that are shot out away from the black hole because it cannot be absorbed quickly enough. An isolated black hole, however, would not have an accretion disk and would only be detectable by gravitational lensing. Cosmologists doubt they make up a majority of dark matter because the black holes are at isolated points of the galaxy. The largest contributor to the missing mass must be spread throughout the galaxy to balance the gravity.

Neutron stars are somewhat like black holes, but are not heavy enough to collapse completely, instead forming into a material rather like that of an atomic nucleus (sometimes informally called neutronium). After sufficient time these stars could radiate away enough energy to become cold enough that they would be too faint to see. Likewise, old white dwarfs may also become cold and dead, eventually becoming black dwarfs, although the universe is not yet old enough for any stars to have reached this stage.

The next candidate for MACHOs are the brown dwarfs mentioned above. Brown dwarfs are sometimes called "failed stars" as they do not have enough mass for nuclear fusion to begin and simply glow a dull brown. Hence, their only source of energy is released through their own gravitational contraction, and may therefore be faintly visible in some circumstances. Most brown dwarfs are about thirteen to seventy-five times the mass of Jupiter.

Theoretical considerations

Theoretical work simultaneously also showed that ancient MACHOs are not likely to account for the large amounts of dark matter now thought to be present in the universe . The Big Bang as it is currently understood simply couldn't produce enough baryons without causing major problems in the observed elemental abundances, including the abundance of deuterium. However, MACHOs may still constitute 20% of the dark matter in the Milky Way Galaxy.