Q:

What actually is the Daru Brahma In the idol of Lord Jagannath?

I have heard that the heart of Lord Krishna which was unburnt is kept inside the idol of Lord Jagannath in Puri. Is it True???? Probably the heart is termed as 'Daru Brahma'. Does anyone know the true story behind?

A:

As we know that the idol of Lord Jagan Natha is reconstructed before every 19 years. This wooden covering is outer shell which is called "Kalevara/kalebara". 
Hence during every new wooden body there must be the transfer of "core inner material" from old to new wooden shell (nabakalevara). 
This happens in very secret manner in the dark new moon midnight. Only selected priests are allowed during this ritual. Some of them cover their eyes with a cloth. 
The inner substance is called "brahma padartha". This is the core of the idol. There are many possible candidates for this brahma padartha as per many folktales and myths. 

This is a secret ritual. The deities have been given 'Golaka Bishrama'
  (eternal rest), after their 19 years play (leela) in universe in
  'Koili Baikuntha' (Burial ground cum garden of the temple), followed
  by 'Brahma Paribartana'. It is also called 'Ghatantara' (change of
  body) because 'Brahma Padartha' (Supreme matter) has already been
  transferred to the newly carved deities from the bellies' of old
  deities. In the dead of the night, the 'Badagrahis' (particular
  servitors assigned with this special task) had performed this strictly
  confidential rite. Besides, all the used utensils and materials
  associated with the deities and their rituals such as cots, beds,
  pillows, Sarathis of old chariots, Dwarapalas (Body Guards), Ghotak
  (horses), Parswa Devata (deities placed at sides), Sua (parrots) and
  Dhwaja Danda (Flag bearing clubs) have also been given final respite
  in the burial ground. The deities have taken their eternal rest in the
  'Mahagarbha' (great hole, specially dug for this purpose in the
  garden) in the temple premises.
Before 'Brahma Paribartan', "Purnahuti" (ultimate offering) in the
  Yanja (fire sacrifice) which was continued for last 11 days in 'Koili
  Baikuntha' had been performed by Gajapati Maharaja of Puri (The king
  of Puri, the first servitor of the Lords). The king entered the Yanja
  Pedestal in 'Koili Baikuntha'  through the south gate of the temple,
  accompanied with other servitors who were assigned to work as
  'Bidyapati', 'Biswabasu' and 'Brahma' etc in the process of
  "Purnahuti". Followed by a series of rituals and conventional
  worships, the temple was made 'Sodha' (Cleansed) and then the 'Brahma
  Paribartan' was started. During the process, four walls of the temple
  were closed and nobody was allowed to remain present, except the
  assigned and authorised servitors. Energy supply was also stopped,
  while shops and markets were closed to make the process entirely
  invisible. 'Deula Karana' watched the situation with sword in his
  hand, standing at the 'Gumuta' (small pathway for entry) where
  'Patitapabana' (representative of Lord Jagannath) is placed. The
  deities in 'Anasara' (hibernation) were offered Bhoga. Daitapatis made
  a 'Mahasnana' (great bath) of 'Chaturdhamurtis' (four idols, newly
  built). Then the new images are given 'Khandua' and 'Senapata'
  (dressing and decoration) and were brought to the 'Anasara Pindi'
  (temporary pedestal). Only four selected servitors performed the
  secret rituals of 'Brahama Paribartan', being made completely
  blindfolded, their hands and feet wrapped with layers of thick silk
  ribbons, so that they could not see or feel the matter. The supreme
  matters were brought from the old deities and were placed on a silver
  pot which was stationed on a 'Khatuli' (small cot). The supreme matter
  was offered perfumes, sandalwood paste, musk and other fragrant
  flowers. Finally it was placed in the bellies of newly carved idols.
  Followed by the 'Brahma Paribartan', the old idols were brought to
  'Koili Baikuntha' for 'Patali' (sacred burial) in 'Mahagarva' (great
  hole).
Any unsolved mystery inevitably gives rise to speculations, myths as
  well as absurdities. There are several theories regarding the identity
  of ‘Brahma padartha’, several of them based on myths. Many believe
  ‘Brahma padartha’ to be the mortal remains of Lord Sri Krishna. This
  belief is rooted in an episode in Odia Mahabharat written by Adikabi
  Sarala Das. Some western researchers have also quoted this theory.
  According to this belief, the body of Sri Krishna did not burn up
  completely despite repeated efforts. Legend has it that the unburnt
  mortal remains of Sri Krishna were flown in the sea and reached the
  Puri coast to be used as ‘Brahma padartha’ of ‘daru’ idols. But this
  belief has no historical basis and is completely based on mythology.
  Moreover, it is quiet illogical to accept that something thrown into
  sea near Dwaraka on the western coast of India could circumnavigate
  around the Indian peninsula to reach the Puri coast on the eastern
  side.
Some others claim ‘Brahma padartha’ may be a tooth of Goutama Buddha.
  As per Buddhist history, a tooth of Buddha collected from his funeral
  pyre by a ‘ther’ named Kshyema. This tooth had reached Kalinga where
  it was worshipped in a city named Dantapura. Historians say this tooth
  is now being worshipped at the ‘Dantamandir’in Kandy in Sri Lanka.
  Kalinga had faced several invasions because of this tooth. Its king
  Guhashiva had been killed in battle. His daughter Hemamala and
  son-in-law Dantakumar had managed to escape to Sri Lanka along with
  the tooth of Buddha. So, this tooth cannot be the ‘Brahma padartha’.
Some claim ‘Brahma padartha’ is actually a ‘shaligram’. To escape the
  devastation caused by sea waves and attacks of Raktabahu, the idols of
  Sri Jagannath temple had been whisked away to Sonepur area in western
  Odisha. Idols were buried deep down the ground. Later king
  Jajatikeshari had recovered remnants of these idols and new idols had
  been constructed to replace them. On the instructions of
  Sankaracharya, a monk named Bharati Acharya had visited Nepal to
  procure two shaligrams. These are thought to be ‘Brahma padartha’. But
  analysts of rituals of Sri Jagannath temple are of the opinion that
  worship of shaligram does not need ‘prana pratistha’ or invocation of
  life. But ‘prana pratistha’ is an integral ritual for deities of Sri
  Jagananth temple.
Another myth regarding ‘Brahma padartha’ is related to Sati and Lord
  Shiva. Shiva was doing tandav carrying corpse of Sati on his
  shoulders. Lord Vishnu cut down Sati’s body into many parts by his
  Sudarshan chakra. Its naval portion fell at Jajpur and was carried by
  river to sea. It was collected from Puri coast and was divided into
  four parts to become ‘Brahma padartha’ of four idols. This again has
  mythological overtones.
Several other objects have been assumed to be ‘Brahma padartha’. They
  include mercury kept in small caskets, miniature idol of a couple in
  sleeping position, tulsi leaves crafted from gold or ‘ashtadhatu’
  alloy.
Another assumption based on circumstantial evidence claims the ‘Brahma
  padartha’ inside idol of Sri Jagannath is  shaligram and a Shri Gopal
  Yantra drawn on gold leaf. Idol of Sri Balabhadra does contain gold
  Shivalinga along with ‘Shaiva Yantra’ as ‘Brahma padartha’. Core
  material in Devi Subhadra is a ‘Bhuvaneswari Yantra’ drawn on gold
  plate and ‘Brahma padartha’ of Sri Sudarshan is a shaligram and ‘Sri
  Nrusimha Yantra’ made up of gold.

Overall, it is not possible to say what exactly is the brahma padartha. But from majority of claims and stories it looks like it is a combination of special "shaligram" along with a sacred "yantra" (sigil).

